diff --git a/README.md b/README.md
index 6ce7dd4..92ac07a 100644
--- a/README.md
+++ b/README.md
@@ -1,27 +1,37 @@
 # CoreLibs for Python
 
-This is a pip package that can be installed into any project and covers the following pars
+> [!warning]
+> This is pre-production, location of methods and names of paths can change
+
+This is a pip package that can be installed into any project and covers the following parts
 
 - logging update with exception logs
 - requests wrapper for easier auth pass on access
 - dict fingerprinting
 - jmespath search
-- dump outputs for data
+- json helpers for conten replace and output
+- dump outputs for data for debugging
 - progress printing
 - string formatting, time creation, byte formatting
+- Enum base class
+- SQLite simple IO class
+- Symmetric encryption
 
 ## Current list
 
 - config_handling: simple INI config file data loader with check/convert/etc
 - csv_handling: csv dict writer helper
 - debug_handling: various debug helpers like data dumper, timer, utilization, etc
+- db_handling: SQLite interface class
+- encyption_handling: symmetric encryption
 - file_handling: crc handling for file content and file names, progress bar
-- json_handling: jmespath support and json date support
+- json_handling: jmespath support and json date support, replace content in dict with json paths
 - iterator_handling: list and dictionary handling support (search, fingerprinting, etc)
 - logging_handling: extend log and also error message handling
 - requests_handling: requests wrapper for better calls with auth headers
 - script_handling: pid lock file handling, abort timer
-- string_handling: byte format, datetime format, hashing, string formats for numbrers, double byte string format, etc
+- string_handling: byte format, datetime format, datetime compare, hashing, string formats for numbers, double byte string format, etc
+- var_handling: var type checkers, enum base class
 
 ## UV setup
 
diff --git a/src/corelibs/datetime_handling/__init__.py b/src/corelibs/datetime_handling/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/corelibs/datetime_handling/datetime_helpers.py b/src/corelibs/datetime_handling/datetime_helpers.py
new file mode 100644
index 0000000..8fd85b0
--- /dev/null
+++ b/src/corelibs/datetime_handling/datetime_helpers.py
@@ -0,0 +1,435 @@
+"""
+Various string based date/time helpers
+"""
+
+import time as time_t
+from datetime import datetime, time
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
+from typing import Callable
+
+DAYS_OF_WEEK_LONG_TO_SHORT: dict[str, str] = {
+    'Monday': 'Mon',
+    'Tuesday': 'Tue',
+    'Wednesay': 'Wed',
+    'Thursday': 'Thu',
+    'Friday': 'Fri',
+    'Saturday': 'Sat',
+    'Sunday': 'Sun',
+}
+DAYS_OF_WEEK_ISO: dict[int, str] = {
+    1: 'Mon', 2: 'Tue', 3: 'Wed', 4: 'Thu', 5: 'Fri', 6: 'Sat', 7: 'Sun'
+}
+DAYS_OF_WEEK_ISO_REVERSED: dict[str, int] = {value: key for key, value in DAYS_OF_WEEK_ISO.items()}
+
+
+def create_time(timestamp: float, timestamp_format: str = "%Y-%m-%d %H:%M:%S") -> str:
+    """
+    just takes a timestamp and prints out humand readable format
+
+    Arguments:
+        timestamp {float} -- _description_
+
+    Keyword Arguments:
+        timestamp_format {_type_} -- _description_ (default: {"%Y-%m-%d %H:%M:%S"})
+
+    Returns:
+        str -- _description_
+    """
+    return time_t.strftime(timestamp_format, time_t.localtime(timestamp))
+
+
+def get_system_timezone():
+    """Get system timezone using datetime's automatic detection"""
+    # Get current time with system timezone
+    local_time = datetime.now().astimezone()
+
+    # Extract timezone info
+    system_tz = local_time.tzinfo
+    timezone_name = str(system_tz)
+
+    return system_tz, timezone_name
+
+
+def parse_timezone_data(timezone_tz: str = '') -> ZoneInfo:
+    """
+    parses a string to get the ZoneInfo
+    If not set or not valid gets local time,
+    if that is not possible get UTC
+
+    Keyword Arguments:
+        timezone_tz {str} -- _description_ (default: {''})
+
+    Returns:
+        ZoneInfo -- _description_
+    """
+    try:
+        return ZoneInfo(timezone_tz)
+    except (ZoneInfoNotFoundError, ValueError, TypeError):
+        # use default
+        time_tz, time_tz_str = get_system_timezone()
+        if time_tz is None:
+            return ZoneInfo('UTC')
+        # TODO build proper TZ lookup
+        tz_mapping = {
+            'JST': 'Asia/Tokyo',
+            'KST': 'Asia/Seoul',
+            'IST': 'Asia/Kolkata',
+            'CST': 'Asia/Shanghai',  # Default to China for CST
+            'AEST': 'Australia/Sydney',
+            'AWST': 'Australia/Perth',
+            'EST': 'America/New_York',
+            'EDT': 'America/New_York',
+            'CDT': 'America/Chicago',
+            'MST': 'America/Denver',
+            'MDT': 'America/Denver',
+            'PST': 'America/Los_Angeles',
+            'PDT': 'America/Los_Angeles',
+            'GMT': 'UTC',
+            'UTC': 'UTC',
+            'CET': 'Europe/Berlin',
+            'CEST': 'Europe/Berlin',
+            'BST': 'Europe/London',
+        }
+        try:
+            return ZoneInfo(tz_mapping[time_tz_str])
+        except (ZoneInfoNotFoundError, IndexError) as e:
+            raise ValueError(f"No mapping for {time_tz_str}: {e}") from e
+
+
+def get_datetime_iso8601(timezone_tz: str | ZoneInfo = '', sep: str = 'T', timespec: str = 'microseconds') -> str:
+    """
+    set a datetime in the iso8601 format with microseconds
+
+    Returns:
+        str -- _description_
+    """
+    # parse if this is a string
+    if isinstance(timezone_tz, str):
+        timezone_tz = parse_timezone_data(timezone_tz)
+    return datetime.now(timezone_tz).isoformat(sep=sep, timespec=timespec)
+
+
+def validate_date(date: str, not_before: datetime | None = None, not_after: datetime | None = None) -> bool:
+    """
+    check if Y-m-d or Y/m/d are parsable and valid
+
+    Arguments:
+        date {str} -- _description_
+
+    Returns:
+        bool -- _description_
+    """
+    formats = ['%Y-%m-%d', '%Y/%m/%d']
+    for __format in formats:
+        try:
+            __date = datetime.strptime(date, __format).date()
+            if not_before is not None and __date < not_before.date():
+                return False
+            if not_after is not None and __date > not_after.date():
+                return False
+            return True
+        except ValueError:
+            continue
+    return False
+
+
+def parse_flexible_date(
+    date_str: str,
+    timezone_tz: str | ZoneInfo | None = None,
+    shift_time_zone: bool = True
+) -> datetime | None:
+    """
+    Parse date string in multiple formats
+    will add time zone info if not None
+    on default it will change the TZ and time to the new time zone
+    if no TZ info is set in date_str, then localtime is assumed
+
+    Arguments:
+        date_str {str} -- _description_
+
+    Keyword Arguments:
+        timezone_tz {str | ZoneInfo | None} -- _description_ (default: {None})
+        shift_time_zone {bool} -- _description_ (default: {True})
+
+    Returns:
+        datetime | None -- _description_
+    """
+
+    date_str = date_str.strip()
+
+    # Try different parsing methods
+    parsers: list[Callable[[str], datetime]] = [
+        # ISO 8601 format
+        lambda x: datetime.fromisoformat(x),  # pylint: disable=W0108
+        # Simple date format
+        lambda x: datetime.strptime(x, "%Y-%m-%d"),
+        # Alternative ISO formats (fallback)
+        lambda x: datetime.strptime(x, "%Y-%m-%dT%H:%M:%S"),
+        lambda x: datetime.strptime(x, "%Y-%m-%dT%H:%M:%S.%f"),
+    ]
+
+    if timezone_tz is not None:
+        if isinstance(timezone_tz, str):
+            timezone_tz = parse_timezone_data(timezone_tz)
+
+    date_new = None
+    for parser in parsers:
+        try:
+            date_new = parser(date_str)
+            break
+        except ValueError:
+            continue
+
+    if date_new is not None:
+        if timezone_tz is not None:
+            # shift time zone (default), this will change the date
+            # if the date has no +HH:MM it will take the local time zone as base
+            if shift_time_zone:
+                return date_new.astimezone(timezone_tz)
+            # just add the time zone
+            return date_new.replace(tzinfo=timezone_tz)
+        return date_new
+
+    return None
+
+
+def compare_dates(date1_str: str, date2_str: str) -> None | bool:
+    """
+    compare two dates, if the first one is newer than the second one return True
+    If the dates are equal then false will be returned
+    on error return None
+
+    Arguments:
+        date1_str {str} -- _description_
+        date2_str {str} -- _description_
+
+    Returns:
+        None | bool -- _description_
+    """
+
+    try:
+        # Parse both dates
+        date1 = parse_flexible_date(date1_str)
+        date2 = parse_flexible_date(date2_str)
+
+        # Check if parsing was successful
+        if date1 is None or date2 is None:
+            return None
+
+        # Compare dates
+        return date1.date() > date2.date()
+
+    except ValueError:
+        return None
+
+
+def find_newest_datetime_in_list(date_list: list[str]) -> None | str:
+    """
+    Find the newest date from a list of ISO 8601 formatted date strings.
+    Handles potential parsing errors gracefully.
+
+    Args:
+        date_list (list): List of date strings in format '2025-08-06T16:17:39.747+09:00'
+
+    Returns:
+        str: The date string with the newest/latest date, or None if list is empty or all dates are invalid
+    """
+    if not date_list:
+        return None
+
+    valid_dates: list[tuple[str, datetime]] = []
+
+    for date_str in date_list:
+        try:
+            # Parse the date string and store both original string and parsed datetime
+            parsed_date = parse_flexible_date(date_str)
+            if parsed_date is None:
+                continue
+            valid_dates.append((date_str, parsed_date))
+        except ValueError:
+            # Skip invalid date strings
+            continue
+
+    if not valid_dates:
+        return None
+
+    # Find the date string with the maximum datetime value
+    newest_date_str: str = max(valid_dates, key=lambda x: x[1])[0]
+
+    return newest_date_str
+
+
+def parse_day_of_week_range(dow_days: str) -> list[tuple[int, str]]:
+    """
+    Parse a day of week list/range string and return a list of tuples with day index and name.
+    Allowed are short (eg Mon) or long names (eg Monday).
+
+    Arguments:
+        dow_days {str} -- A comma-separated list of days or ranges (e.g., "Mon,Wed-Fri")
+
+    Raises:
+        ValueError: If the input format is invalid or if duplicate days are found.
+
+    Returns:
+        list[tuple[int, str]] -- A list of tuples containing the day index and name.
+    """
+    # we have Sun twice because it can be 0 or 7
+    # Mon is 1 and Sun is 7, which is ISO standard
+    dow_day = dow_days.split(",")
+    dow_day = [day.strip() for day in dow_day if day.strip()]
+    __out_dow_days: list[tuple[int, str]] = []
+    for __dow_day in dow_day:
+        # if we have a "-" in there fill
+        if "-" in __dow_day:
+            __dow_range = __dow_day.split("-")
+            __dow_range = [day.strip().capitalize() for day in __dow_range if day.strip()]
+            try:
+                start_day = DAYS_OF_WEEK_ISO_REVERSED[__dow_range[0]]
+                end_day = DAYS_OF_WEEK_ISO_REVERSED[__dow_range[1]]
+            except KeyError:
+                # try long time
+                try:
+                    start_day = DAYS_OF_WEEK_ISO_REVERSED[DAYS_OF_WEEK_LONG_TO_SHORT[__dow_range[0]]]
+                    end_day = DAYS_OF_WEEK_ISO_REVERSED[DAYS_OF_WEEK_LONG_TO_SHORT[__dow_range[1]]]
+                except KeyError as e:
+                    raise ValueError(f"Invalid day of week entry found: {__dow_day}: {e}") from e
+            # Check if this spans across the weekend (e.g., Fri-Mon)
+            if start_day > end_day:
+                # Handle weekend-spanning range: start_day to 7, then 1 to end_day
+                __out_dow_days.extend(
+                    [
+                        (i, DAYS_OF_WEEK_ISO[i])
+                        for i in range(start_day, 8)  # start_day to Sunday (7)
+                    ]
+                )
+                __out_dow_days.extend(
+                    [
+                        (i, DAYS_OF_WEEK_ISO[i])
+                        for i in range(1, end_day + 1)  # Monday (1) to end_day
+                    ]
+                )
+            else:
+                # Normal range: start_day to end_day
+                __out_dow_days.extend(
+                    [
+                        (i, DAYS_OF_WEEK_ISO[i])
+                        for i in range(start_day, end_day + 1)
+                    ]
+                )
+        else:
+            try:
+                __out_dow_days.append((DAYS_OF_WEEK_ISO_REVERSED[__dow_day], __dow_day))
+            except KeyError as e:
+                raise ValueError(f"Invalid day of week entry found: {__dow_day}: {e}") from e
+    # if there are duplicates, alert
+    if len(__out_dow_days) != len(set(__out_dow_days)):
+        raise ValueError(f"Duplicate day of week entries found: {__out_dow_days}")
+
+    return __out_dow_days
+
+
+def parse_time_range(time_str: str, time_format: str = "%H:%M") -> tuple[time, time]:
+    """
+    Parse a time range string in the format "HH:MM-HH:MM" and return a tuple of two time objects.
+
+    Arguments:
+        time_str {str} -- The time range string to parse.
+
+    Raises:
+        ValueError: Invalid time block set
+        ValueError: Invalid time format
+        ValueError: Start time must be before end time
+
+    Returns:
+        tuple[time, time] -- start time, end time: leading zeros formattd
+    """
+    __time_str = time_str.strip()
+    # split by "-"
+    __time_split = __time_str.split("-")
+    if len(__time_split) != 2:
+        raise ValueError(f"Invalid time block: {__time_str}")
+    try:
+        __time_start = datetime.strptime(__time_split[0], time_format).time()
+        __time_end = datetime.strptime(__time_split[1], time_format).time()
+    except ValueError as e:
+        raise ValueError(f"Invalid time block format [{__time_str}]: {e}") from e
+    if __time_start >= __time_end:
+        raise ValueError(f"Invalid time block set, start time after end time or equal: {__time_str}")
+
+    return __time_start, __time_end
+
+
+def times_overlap_or_connect(time1: tuple[time, time], time2: tuple[time, time], allow_touching: bool = False) -> bool:
+    """
+    Check if two time ranges overlap or connect
+
+    Args:
+        time1 (tuple): (start_time, end_time) for first range
+        time2 (tuple): (start_time, end_time) for second range
+        allow_touching (bool): If True, touching ranges (e.g., 8:00-10:00 and 10:00-12:00) are allowed
+
+    Returns:
+        bool: True if ranges overlap or connect (based on allow_touching)
+    """
+    start1, end1 = time1
+    start2, end2 = time2
+
+    if allow_touching:
+        # Only check for actual overlap (touching is OK)
+        return start1 < end2 and start2 < end1
+    # Check for overlap OR touching
+    return start1 <= end2 and start2 <= end1
+
+
+def is_time_in_range(current_time: str, start_time: str, end_time: str) -> bool:
+    """
+    Check if current_time is within start_time and end_time (inclusive)
+    Time format: "HH:MM" (24-hour format)
+
+    Arguments:
+        current_time {str} -- _description_
+        start_time {str} -- _description_
+        end_time {str} -- _description_
+
+    Returns:
+        bool -- _description_
+    """
+    # Convert string times to time objects
+    current = datetime.strptime(current_time, "%H:%M:%S").time()
+    start = datetime.strptime(start_time, "%H:%M:%S").time()
+    end = datetime.strptime(end_time, "%H:%M:%S").time()
+
+    # Handle case where range crosses midnight (e.g., 22:00 to 06:00)
+    if start <= end:
+        # Normal case: start time is before end time
+        return start <= current <= end
+    # Crosses midnight: e.g., 22:00 to 06:00
+    return current >= start or current <= end
+
+
+def reorder_weekdays_from_today(base_day: str) -> dict[int, str]:
+    """
+    Reorder the days of the week starting from the specified base_day.
+
+    Arguments:
+        base_day {str} -- The day to start the week from (e.g., "Mon").
+
+    Returns:
+        dict[int, str] -- A dictionary mapping day numbers to day names.
+    """
+    try:
+        today_num = DAYS_OF_WEEK_ISO_REVERSED[base_day]
+    except KeyError:
+        try:
+            today_num = DAYS_OF_WEEK_ISO_REVERSED[DAYS_OF_WEEK_LONG_TO_SHORT[base_day]]
+        except KeyError as e:
+            raise ValueError(f"Invalid day name provided: {base_day}: {e}") from e
+    # Convert to list of tuples
+    items = list(DAYS_OF_WEEK_ISO.items())
+    # Reorder: from today onwards + from beginning to yesterday
+    reordered_items = items[today_num - 1:] + items[:today_num - 1]
+
+    # Convert back to dictionary
+    return dict(reordered_items)
+
+# __END__
diff --git a/src/corelibs/string_handling/timestamp_strings.py b/src/corelibs/datetime_handling/timestamp_convert.py
similarity index 70%
rename from src/corelibs/string_handling/timestamp_strings.py
rename to src/corelibs/datetime_handling/timestamp_convert.py
index 22b9b50..8e3974d 100644
--- a/src/corelibs/string_handling/timestamp_strings.py
+++ b/src/corelibs/datetime_handling/timestamp_convert.py
@@ -1,10 +1,9 @@
 """
-Current timestamp strings and time zones
+Convert timestamp strings with time units into seconds and vice versa.
 """
 
+from math import floor
 import re
-from datetime import datetime
-from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 from corelibs.var_handling.var_helpers import is_float
 
 
@@ -16,30 +15,6 @@ class TimeUnitError(Exception):
     """Custom exception for time parsing errors."""
 
 
-class TimestampStrings:
-    """
-    set default time stamps
-    """
-
-    TIME_ZONE: str = 'Asia/Tokyo'
-
-    def __init__(self, time_zone: str | ZoneInfo | None = None):
-        self.timestamp_now = datetime.now()
-        # set time zone as string
-        time_zone = time_zone if time_zone is not None else self.TIME_ZONE
-        self.time_zone = str(time_zone) if not isinstance(time_zone, str) else time_zone
-        # set ZoneInfo type
-        try:
-            self.time_zone_zi = ZoneInfo(self.time_zone)
-        except ZoneInfoNotFoundError as e:
-            raise ValueError(f'Zone could not be loaded [{self.time_zone}]: {e}') from e
-        self.timestamp_now_tz = datetime.now(self.time_zone_zi)
-        self.today = self.timestamp_now.strftime('%Y-%m-%d')
-        self.timestamp = self.timestamp_now.strftime("%Y-%m-%d %H:%M:%S")
-        self.timestamp_tz = self.timestamp_now_tz.strftime("%Y-%m-%d %H:%M:%S %Z")
-        self.timestamp_file = self.timestamp_now.strftime("%Y-%m-%d_%H%M%S")
-
-
 def convert_to_seconds(time_string: str | int | float) -> int:
     """
     Conver a string with time units into a seconds string
@@ -124,7 +99,10 @@ def convert_to_seconds(time_string: str | int | float) -> int:
 def seconds_to_string(seconds: str | int | float, show_microseconds: bool = False) -> str:
     """
     Convert seconds to compact human readable format (e.g., "1d 2h 3m 4.567s")
+    Zero values are omitted.
+    milliseconds if requested are added as fractional part of seconds.
     Supports negative values with "-" prefix
+    if not int or float, will return as is
 
     Args:
         seconds (float): Time in seconds (can be negative)
@@ -172,4 +150,51 @@ def seconds_to_string(seconds: str | int | float, show_microseconds: bool = Fals
     result = " ".join(parts)
     return f"-{result}" if negative else result
 
+
+def convert_timestamp(timestamp: float | int | str, show_microseconds: bool = True) -> str:
+    """
+    format timestamp into human readable format. This function will add 0 values between set values
+    for example if we have 1d 1s it would output 1d 0h 0m 1s
+    Milliseconds will be shown if set, and added with ms at the end
+    Negative values will be prefixed with "-"
+    if not int or float, will return as is
+
+    Arguments:
+        timestamp {float} -- _description_
+
+    Keyword Arguments:
+        show_micro {bool} -- _description_ (default: {True})
+
+    Returns:
+        str -- _description_
+    """
+    if not isinstance(timestamp, (int, float)):
+        return timestamp
+    # cut of the ms, but first round them up to four
+    __timestamp_ms_split = str(round(timestamp, 4)).split(".")
+    timestamp = int(__timestamp_ms_split[0])
+    negative = timestamp < 0
+    timestamp = abs(timestamp)
+    try:
+        ms = int(__timestamp_ms_split[1])
+    except IndexError:
+        ms = 0
+    timegroups = (86400, 3600, 60, 1)
+    output: list[int] = []
+    for i in timegroups:
+        output.append(int(floor(timestamp / i)))
+        timestamp = timestamp % i
+    # output has days|hours|min|sec ms
+    time_string = ""
+    if output[0]:
+        time_string = f"{output[0]}d "
+    if output[0] or output[1]:
+        time_string += f"{output[1]}h "
+    if output[0] or output[1] or output[2]:
+        time_string += f"{output[2]}m "
+    time_string += f"{output[3]}s"
+    if show_microseconds:
+        time_string += f" {ms}ms" if ms else " 0ms"
+    return f"-{time_string}" if negative else time_string
+
 # __END__
diff --git a/src/corelibs/datetime_handling/timestamp_strings.py b/src/corelibs/datetime_handling/timestamp_strings.py
new file mode 100644
index 0000000..6aa3f80
--- /dev/null
+++ b/src/corelibs/datetime_handling/timestamp_strings.py
@@ -0,0 +1,32 @@
+"""
+Current timestamp strings and time zones
+"""
+
+from datetime import datetime
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
+
+
+class TimestampStrings:
+    """
+    set default time stamps
+    """
+
+    TIME_ZONE: str = 'Asia/Tokyo'
+
+    def __init__(self, time_zone: str | ZoneInfo | None = None):
+        self.timestamp_now = datetime.now()
+        # set time zone as string
+        time_zone = time_zone if time_zone is not None else self.TIME_ZONE
+        self.time_zone = str(time_zone) if not isinstance(time_zone, str) else time_zone
+        # set ZoneInfo type
+        try:
+            self.time_zone_zi = ZoneInfo(self.time_zone)
+        except ZoneInfoNotFoundError as e:
+            raise ValueError(f'Zone could not be loaded [{self.time_zone}]: {e}') from e
+        self.timestamp_now_tz = datetime.now(self.time_zone_zi)
+        self.today = self.timestamp_now.strftime('%Y-%m-%d')
+        self.timestamp = self.timestamp_now.strftime("%Y-%m-%d %H:%M:%S")
+        self.timestamp_tz = self.timestamp_now_tz.strftime("%Y-%m-%d %H:%M:%S %Z")
+        self.timestamp_file = self.timestamp_now.strftime("%Y-%m-%d_%H%M%S")
+
+# __END__
diff --git a/src/corelibs/file_handling/progress.py b/src/corelibs/file_handling/progress.py
index caa0cd7..fde5f7d 100644
--- a/src/corelibs/file_handling/progress.py
+++ b/src/corelibs/file_handling/progress.py
@@ -32,7 +32,7 @@ show_position(file pos optional)
 import time
 from typing import Literal
 from math import floor
-from corelibs.string_handling.datetime_helpers import convert_timestamp
+from corelibs.datetime_handling.datetime_helpers import convert_timestamp
 from corelibs.string_handling.byte_helpers import format_bytes
 
 
diff --git a/src/corelibs/string_handling/datetime_helpers.py b/src/corelibs/string_handling/datetime_helpers.py
deleted file mode 100644
index 1694cd0..0000000
--- a/src/corelibs/string_handling/datetime_helpers.py
+++ /dev/null
@@ -1,136 +0,0 @@
-"""
-Various string based date/time helpers
-"""
-
-from math import floor
-import time as time_t
-from datetime import datetime
-from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
-
-
-def convert_timestamp(timestamp: float | int, show_micro: bool = True) -> str:
-    """
-    format timestamp into human readable format
-
-    Arguments:
-        timestamp {float} -- _description_
-
-    Keyword Arguments:
-        show_micro {bool} -- _description_ (default: {True})
-
-    Returns:
-        str -- _description_
-    """
-    # cut of the ms, but first round them up to four
-    __timestamp_ms_split = str(round(timestamp, 4)).split(".")
-    timestamp = int(__timestamp_ms_split[0])
-    try:
-        ms = int(__timestamp_ms_split[1])
-    except IndexError:
-        ms = 0
-    timegroups = (86400, 3600, 60, 1)
-    output: list[int] = []
-    for i in timegroups:
-        output.append(int(floor(timestamp / i)))
-        timestamp = timestamp % i
-    # output has days|hours|min|sec ms
-    time_string = ""
-    if output[0]:
-        time_string = f"{output[0]}d"
-    if output[0] or output[1]:
-        time_string += f"{output[1]}h "
-    if output[0] or output[1] or output[2]:
-        time_string += f"{output[2]}m "
-    time_string += f"{output[3]}s"
-    if show_micro:
-        time_string += f" {ms}ms" if ms else " 0ms"
-    return time_string
-
-
-def create_time(timestamp: float, timestamp_format: str = "%Y-%m-%d %H:%M:%S") -> str:
-    """
-    just takes a timestamp and prints out humand readable format
-
-    Arguments:
-        timestamp {float} -- _description_
-
-    Keyword Arguments:
-        timestamp_format {_type_} -- _description_ (default: {"%Y-%m-%d %H:%M:%S"})
-
-    Returns:
-        str -- _description_
-    """
-    return time_t.strftime(timestamp_format, time_t.localtime(timestamp))
-
-
-def get_system_timezone():
-    """Get system timezone using datetime's automatic detection"""
-    # Get current time with system timezone
-    local_time = datetime.now().astimezone()
-
-    # Extract timezone info
-    system_tz = local_time.tzinfo
-    timezone_name = str(system_tz)
-
-    return system_tz, timezone_name
-
-
-def parse_timezone_data(timezone_tz: str = '') -> ZoneInfo:
-    """
-    parses a string to get the ZoneInfo
-    If not set or not valid gets local time,
-    if that is not possible get UTC
-
-    Keyword Arguments:
-        timezone_tz {str} -- _description_ (default: {''})
-
-    Returns:
-        ZoneInfo -- _description_
-    """
-    try:
-        return ZoneInfo(timezone_tz)
-    except (ZoneInfoNotFoundError, ValueError, TypeError):
-        # use default
-        time_tz, time_tz_str = get_system_timezone()
-        if time_tz is None:
-            return ZoneInfo('UTC')
-        # TODO build proper TZ lookup
-        tz_mapping = {
-            'JST': 'Asia/Tokyo',
-            'KST': 'Asia/Seoul',
-            'IST': 'Asia/Kolkata',
-            'CST': 'Asia/Shanghai',  # Default to China for CST
-            'AEST': 'Australia/Sydney',
-            'AWST': 'Australia/Perth',
-            'EST': 'America/New_York',
-            'EDT': 'America/New_York',
-            'CDT': 'America/Chicago',
-            'MST': 'America/Denver',
-            'MDT': 'America/Denver',
-            'PST': 'America/Los_Angeles',
-            'PDT': 'America/Los_Angeles',
-            'GMT': 'UTC',
-            'UTC': 'UTC',
-            'CET': 'Europe/Berlin',
-            'CEST': 'Europe/Berlin',
-            'BST': 'Europe/London',
-        }
-        try:
-            return ZoneInfo(tz_mapping[time_tz_str])
-        except (ZoneInfoNotFoundError, IndexError) as e:
-            raise ValueError(f"No mapping for {time_tz_str}: {e}") from e
-
-
-def get_datetime_iso8601(timezone_tz: str | ZoneInfo = '', sep: str = 'T', timespec: str = 'microseconds') -> str:
-    """
-    set a datetime in the iso8601 format with microseconds
-
-    Returns:
-        str -- _description_
-    """
-    # parse if this is a string
-    if isinstance(timezone_tz, str):
-        timezone_tz = parse_timezone_data(timezone_tz)
-    return datetime.now(timezone_tz).isoformat(sep=sep, timespec=timespec)
-
-# __END__
diff --git a/test-run/datetime_handling/datetime_helpers.py b/test-run/datetime_handling/datetime_helpers.py
new file mode 100644
index 0000000..7e89657
--- /dev/null
+++ b/test-run/datetime_handling/datetime_helpers.py
@@ -0,0 +1,236 @@
+#!/usr/bin/env python3
+
+"""
+date string helper test
+"""
+
+from datetime import datetime
+from corelibs.datetime_handling.datetime_helpers import (
+    get_datetime_iso8601, get_system_timezone, parse_timezone_data, validate_date,
+    parse_flexible_date, compare_dates, find_newest_datetime_in_list,
+    parse_day_of_week_range, parse_time_range, times_overlap_or_connect, is_time_in_range,
+    reorder_weekdays_from_today
+)
+
+
+def __get_datetime_iso8601():
+    """
+    Comment
+    """
+    for tz in [
+        '', 'Asia/Tokyo', 'UTC', 'Europe/Vienna',
+        'America/New_York', 'Australia/Sydney',
+        'invalid'
+    ]:
+        print(f"{tz} -> {get_datetime_iso8601(tz)}")
+
+
+def __parse_timezone_data():
+    for tz in [
+        'JST', 'KST', 'UTC', 'CET', 'CEST',
+    ]:
+        print(f"{tz} -> {parse_timezone_data(tz)}")
+
+
+def __validate_date():
+    """
+    Comment
+    """
+
+    test_dates = [
+        "2024-01-01",
+        "2024-02-29",  # Leap year
+        "2023-02-29",  # Invalid date
+        "2024-13-01",  # Invalid month
+        "2024-00-10",  # Invalid month
+        "2024-04-31",  # Invalid day
+        "invalid-date"
+    ]
+
+    for date_str in test_dates:
+        is_valid = validate_date(date_str)
+        print(f"Date '{date_str}' is valid: {is_valid}")
+
+    # also test not before and not after
+    not_before_dates = [
+        "2023-12-31",
+        "2024-01-01",
+        "2024-02-29",
+    ]
+    not_after_dates = [
+        "2024-12-31",
+        "2024-11-30",
+        "2025-01-01",
+    ]
+
+    for date_str in not_before_dates:
+        datetime.strptime(date_str, "%Y-%m-%d")  # Ensure valid date format
+        is_valid = validate_date(date_str, not_before=datetime.strptime("2024-01-01", "%Y-%m-%d"))
+        print(f"Date '{date_str}' is valid (not before 2024-01-01): {is_valid}")
+
+    for date_str in not_after_dates:
+        is_valid = validate_date(date_str, not_after=datetime.strptime("2024-12-31", "%Y-%m-%d"))
+        print(f"Date '{date_str}' is valid (not after 2024-12-31): {is_valid}")
+
+    for date_str in test_dates:
+        is_valid = validate_date(
+            date_str,
+            not_before=datetime.strptime("2024-01-01", "%Y-%m-%d"),
+            not_after=datetime.strptime("2024-12-31", "%Y-%m-%d")
+        )
+        print(f"Date '{date_str}' is valid (2024 only): {is_valid}")
+
+
+def __parse_flexible_date():
+    for date_str in [
+        "2024-01-01",
+        "01/02/2024",
+        "February 29, 2024",
+        "Invalid date",
+        "2025-01-01 12:18:10",
+        "2025-01-01 12:18:10.566",
+        "2025-01-01T12:18:10.566",
+        "2025-01-01T12:18:10.566+02:00",
+    ]:
+        print(f"{date_str} -> {parse_flexible_date(date_str)}")
+
+
+def __compare_dates():
+
+    for date1, date2 in [
+        ("2024-01-01 12:00:00", "2024-01-01 15:30:00"),
+        ("2024-01-02", "2024-01-01"),
+        ("2024-01-01T10:00:00+02:00", "2024-01-01T08:00:00Z"),
+        ("invalid-date", "2024-01-01"),
+        ("2024-01-01", "invalid-date"),
+        ("invalid-date", "also-invalid"),
+    ]:
+        result = compare_dates(date1, date2)
+        print(f"Comparing '{date1}' and '{date2}': {result}")
+
+
+def __find_newest_datetime_in_list():
+    date_list = [
+        "2024-01-01 12:00:00",
+        "2024-01-02 09:30:00",
+        "2023-12-31 23:59:59",
+        "2024-01-02 15:45:00",
+        "2024-01-02T15:45:00.001",
+        "invalid-date",
+    ]
+    newest_date = find_newest_datetime_in_list(date_list)
+    print(f"Newest date in list: {newest_date}")
+
+
+def __parse_day_of_week_range():
+    ranges = [
+        "Mon-Fri",
+        "Saturday-Sunday",
+        "Wed-Mon",
+        "Fri-Fri",
+        "mon-tue",
+        "Invalid-Range"
+    ]
+    for range_str in ranges:
+        try:
+            days = parse_day_of_week_range(range_str)
+            print(f"Day range '{range_str}' -> {days}")
+        except ValueError as e:
+            print(f"[!] Error parsing day range '{range_str}': {e}")
+
+
+def __parse_time_range():
+    ranges = [
+        "08:00-17:00",
+        "22:00-06:00",
+        "12:30-12:30",
+        "invalid-range"
+    ]
+    for range_str in ranges:
+        try:
+            start_time, end_time = parse_time_range(range_str)
+            print(f"Time range '{range_str}' -> Start: {start_time}, End: {end_time}")
+        except ValueError as e:
+            print(f"[!] Error parsing time range '{range_str}': {e}")
+
+
+def __times_overlap_or_connect():
+    time_format = "%H:%M"
+    time_ranges = [
+        (("08:00", "12:00"), ("11:00", "15:00")),  # Overlap
+        (("22:00", "02:00"), ("01:00", "05:00")),  # Overlap across midnight
+        (("10:00", "12:00"), ("12:00", "14:00")),  # Connect
+        (("09:00", "11:00"), ("12:00", "14:00")),  # No overlap
+    ]
+    for (start1, end1), (start2, end2) in time_ranges:
+        start1 = datetime.strptime(start1, time_format).time()
+        end1 = datetime.strptime(end1, time_format).time()
+        start2 = datetime.strptime(start2, time_format).time()
+        end2 = datetime.strptime(end2, time_format).time()
+        overlap = times_overlap_or_connect((start1, end1), (start2, end2))
+        overlap_connect = times_overlap_or_connect((start1, end1), (start2, end2), True)
+        print(f"Time ranges {start1}-{end1} and {start2}-{end2} overlap/connect: {overlap}/{overlap_connect}")
+
+
+def __is_time_in_range():
+    time_format = "%H:%M:%S"
+    test_cases = [
+        ("10:00:00", "09:00:00", "11:00:00"),
+        ("23:30:00", "22:00:00", "01:00:00"),  # Across midnight
+        ("05:00:00", "06:00:00", "10:00:00"),  # Not in range
+        ("12:00:00", "12:00:00", "12:00:00"),  # Exact match
+    ]
+    for (check_time, start_time, end_time) in test_cases:
+        start_time = datetime.strptime(start_time, time_format).time()
+        end_time = datetime.strptime(end_time, time_format).time()
+        in_range = is_time_in_range(
+            f"{check_time}", start_time.strftime("%H:%M:%S"), end_time.strftime("%H:%M:%S")
+        )
+        print(f"Time {check_time} in range {start_time}-{end_time}: {in_range}")
+
+
+def __reorder_weekdays_from_today():
+    for base_day in [
+        "Tue", "Wed", "Sunday", "Fri", "InvalidDay"
+    ]:
+        try:
+            reordered_days = reorder_weekdays_from_today(base_day)
+            print(f"Reordered weekdays from {base_day}: {reordered_days}")
+        except ValueError as e:
+            print(f"[!] Error reordering weekdays from '{base_day}': {e}")
+
+
+def main() -> None:
+    """
+    Comment
+    """
+    print("\nDatetime ISO 8601 tests:\n")
+    __get_datetime_iso8601()
+    print("\nSystem time test:")
+    print(f"System time: {get_system_timezone()}")
+    print("\nParse timezone data tests:\n")
+    __parse_timezone_data()
+    print("\nValidate date tests:\n")
+    __validate_date()
+    print("\nParse flexible date tests:\n")
+    __parse_flexible_date()
+    print("\nCompare dates tests:\n")
+    __compare_dates()
+    print("\nFind newest datetime in list tests:\n")
+    __find_newest_datetime_in_list()
+    print("\nParse day of week range tests:\n")
+    __parse_day_of_week_range()
+    print("\nParse time range tests:\n")
+    __parse_time_range()
+    print("\nTimes overlap or connect tests:\n")
+    __times_overlap_or_connect()
+    print("\nIs time in range tests:\n")
+    __is_time_in_range()
+    print("\nReorder weekdays from today tests:\n")
+    __reorder_weekdays_from_today()
+
+
+if __name__ == "__main__":
+    main()
+
+# __END__
diff --git a/test-run/string_handling/timestamp_strings.py b/test-run/datetime_handling/timestamp_convert.py
similarity index 89%
rename from test-run/string_handling/timestamp_strings.py
rename to test-run/datetime_handling/timestamp_convert.py
index a018381..34b715e 100644
--- a/test-run/string_handling/timestamp_strings.py
+++ b/test-run/datetime_handling/timestamp_convert.py
@@ -4,8 +4,8 @@
 timestamp string checks
 """
 
-from corelibs.string_handling.timestamp_strings import (
-    seconds_to_string, convert_to_seconds, TimeParseError, TimeUnitError
+from corelibs.datetime_handling.timestamp_convert import (
+    convert_timestamp, seconds_to_string, convert_to_seconds, TimeParseError, TimeUnitError
 )
 
 
@@ -13,6 +13,7 @@ def main() -> None:
     """
     Comment
     """
+    print("\n--- Testing convert_to_seconds ---\n")
     test_cases = [
         "5M 6d",           # 5 months, 6 days
         "2h 30m 45s",      # 2 hours, 30 minutes, 45 seconds
@@ -58,6 +59,8 @@ def main() -> None:
         except (TimeParseError, TimeUnitError) as e:
             print(f"Error encountered for {time_string}: {type(e).__name__}: {e}")
 
+    print("\n--- Testing seconds_to_string and convert_timestamp ---\n")
+
     test_values = [
         'as is string',
         -172800.001234,  # -2 days, -0.001234 seconds
@@ -79,7 +82,8 @@ def main() -> None:
 
     for time_value in test_values:
         result = seconds_to_string(time_value, show_microseconds=True)
-        print(f"Seconds to human readable: {time_value} => {result}")
+        result_alt = convert_timestamp(time_value, show_microseconds=True)
+        print(f"Seconds to human readable: {time_value} => {result} / {result_alt}")
 
 
 if __name__ == "__main__":
diff --git a/test-run/progress/progress_test.py b/test-run/progress/progress_test.py
index a7938a4..334b9aa 100755
--- a/test-run/progress/progress_test.py
+++ b/test-run/progress/progress_test.py
@@ -10,7 +10,8 @@ import sys
 import io
 from pathlib import Path
 from corelibs.file_handling.progress import Progress
-from corelibs.string_handling.datetime_helpers import convert_timestamp, create_time
+from corelibs.datetime_handling.datetime_helpers import create_time
+from corelibs.datetime_handling.timestamp_convert import convert_timestamp
 
 
 def main():
diff --git a/test-run/string_handling/datetime_helpers.py b/test-run/string_handling/datetime_helpers.py
deleted file mode 100644
index 5a60666..0000000
--- a/test-run/string_handling/datetime_helpers.py
+++ /dev/null
@@ -1,26 +0,0 @@
-#!/usr/bin/env python3
-
-"""
-date string helper test
-"""
-
-from corelibs.string_handling.datetime_helpers import get_datetime_iso8601
-
-
-def main() -> None:
-    """
-    Comment
-    """
-    print(get_datetime_iso8601())
-    print(get_datetime_iso8601('Asia/Tokyo'))
-    print(get_datetime_iso8601('UTC'))
-    print(get_datetime_iso8601('Europe/Vienna'))
-    print(get_datetime_iso8601('America/New_York'))
-    print(get_datetime_iso8601('Australia/Sydney'))
-    print(get_datetime_iso8601('invalid'))
-
-
-if __name__ == "__main__":
-    main()
-
-# __END__
diff --git a/test-run/timestamp_strings/timestamp_strings.py b/test-run/timestamp_strings/timestamp_strings.py
index b4fd464..d664cd8 100644
--- a/test-run/timestamp_strings/timestamp_strings.py
+++ b/test-run/timestamp_strings/timestamp_strings.py
@@ -5,7 +5,7 @@ Test for double byte format
 """
 
 from zoneinfo import ZoneInfo
-from corelibs.string_handling.timestamp_strings import TimestampStrings
+from corelibs.datetime_handling.timestamp_strings import TimestampStrings
 
 
 def main():
diff --git a/tests/unit/datetime_handling/__init__.py b/tests/unit/datetime_handling/__init__.py
new file mode 100644
index 0000000..a81225c
--- /dev/null
+++ b/tests/unit/datetime_handling/__init__.py
@@ -0,0 +1,3 @@
+"""
+Unit tests for encryption_handling module
+"""
diff --git a/tests/unit/string_handling/test_convert_to_seconds.py b/tests/unit/datetime_handling/test_convert_to_seconds.py
similarity index 98%
rename from tests/unit/string_handling/test_convert_to_seconds.py
rename to tests/unit/datetime_handling/test_convert_to_seconds.py
index cd0991c..f2a7325 100644
--- a/tests/unit/string_handling/test_convert_to_seconds.py
+++ b/tests/unit/datetime_handling/test_convert_to_seconds.py
@@ -3,7 +3,7 @@ Unit tests for convert_to_seconds function from timestamp_strings module.
 """
 
 import pytest
-from corelibs.string_handling.timestamp_strings import convert_to_seconds, TimeParseError, TimeUnitError
+from corelibs.datetime_handling.timestamp_convert import convert_to_seconds, TimeParseError, TimeUnitError
 
 
 class TestConvertToSeconds:
diff --git a/tests/unit/datetime_handling/test_datetime_helpers.py b/tests/unit/datetime_handling/test_datetime_helpers.py
new file mode 100644
index 0000000..ce13b3f
--- /dev/null
+++ b/tests/unit/datetime_handling/test_datetime_helpers.py
@@ -0,0 +1,690 @@
+"""
+PyTest: datetime_handling/datetime_helpers
+"""
+
+from datetime import datetime, time
+from zoneinfo import ZoneInfo
+import pytest
+
+from corelibs.datetime_handling.datetime_helpers import (
+    create_time,
+    get_system_timezone,
+    parse_timezone_data,
+    get_datetime_iso8601,
+    validate_date,
+    parse_flexible_date,
+    compare_dates,
+    find_newest_datetime_in_list,
+    parse_day_of_week_range,
+    parse_time_range,
+    times_overlap_or_connect,
+    is_time_in_range,
+    reorder_weekdays_from_today,
+    DAYS_OF_WEEK_LONG_TO_SHORT,
+    DAYS_OF_WEEK_ISO,
+    DAYS_OF_WEEK_ISO_REVERSED,
+)
+
+
+class TestConstants:
+    """Test suite for module constants"""
+
+    def test_days_of_week_long_to_short(self):
+        """Test DAYS_OF_WEEK_LONG_TO_SHORT dictionary"""
+        assert DAYS_OF_WEEK_LONG_TO_SHORT['Monday'] == 'Mon'
+        assert DAYS_OF_WEEK_LONG_TO_SHORT['Tuesday'] == 'Tue'
+        assert DAYS_OF_WEEK_LONG_TO_SHORT['Friday'] == 'Fri'
+        assert DAYS_OF_WEEK_LONG_TO_SHORT['Sunday'] == 'Sun'
+        assert len(DAYS_OF_WEEK_LONG_TO_SHORT) == 7
+
+    def test_days_of_week_iso(self):
+        """Test DAYS_OF_WEEK_ISO dictionary"""
+        assert DAYS_OF_WEEK_ISO[1] == 'Mon'
+        assert DAYS_OF_WEEK_ISO[5] == 'Fri'
+        assert DAYS_OF_WEEK_ISO[7] == 'Sun'
+        assert len(DAYS_OF_WEEK_ISO) == 7
+
+    def test_days_of_week_iso_reversed(self):
+        """Test DAYS_OF_WEEK_ISO_REVERSED dictionary"""
+        assert DAYS_OF_WEEK_ISO_REVERSED['Mon'] == 1
+        assert DAYS_OF_WEEK_ISO_REVERSED['Fri'] == 5
+        assert DAYS_OF_WEEK_ISO_REVERSED['Sun'] == 7
+        assert len(DAYS_OF_WEEK_ISO_REVERSED) == 7
+
+
+class TestCreateTime:
+    """Test suite for create_time function"""
+
+    def test_create_time_default_format(self):
+        """Test create_time with default format"""
+        timestamp = 1609459200.0  # 2021-01-01 00:00:00 UTC
+        result = create_time(timestamp)
+        # Result depends on system timezone, so just check format
+        assert len(result) == 19
+        assert '-' in result
+        assert ':' in result
+
+    def test_create_time_custom_format(self):
+        """Test create_time with custom format"""
+        timestamp = 1609459200.0
+        result = create_time(timestamp, "%Y/%m/%d")
+        # Check basic format structure
+        assert '/' in result
+        assert len(result) == 10
+
+    def test_create_time_with_microseconds(self):
+        """Test create_time with microseconds in format"""
+        timestamp = 1609459200.123456
+        result = create_time(timestamp, "%Y-%m-%d %H:%M:%S")
+        assert len(result) == 19
+
+
+class TestGetSystemTimezone:
+    """Test suite for get_system_timezone function"""
+
+    def test_get_system_timezone_returns_tuple(self):
+        """Test that get_system_timezone returns a tuple"""
+        result = get_system_timezone()
+        assert isinstance(result, tuple)
+        assert len(result) == 2
+
+    def test_get_system_timezone_returns_valid_data(self):
+        """Test that get_system_timezone returns valid timezone info"""
+        system_tz, timezone_name = get_system_timezone()
+        assert system_tz is not None
+        assert isinstance(timezone_name, str)
+        assert len(timezone_name) > 0
+
+
+class TestParseTimezoneData:
+    """Test suite for parse_timezone_data function"""
+
+    def test_parse_timezone_data_valid_timezone(self):
+        """Test parse_timezone_data with valid timezone string"""
+        result = parse_timezone_data('Asia/Tokyo')
+        assert isinstance(result, ZoneInfo)
+        assert str(result) == 'Asia/Tokyo'
+
+    def test_parse_timezone_data_utc(self):
+        """Test parse_timezone_data with UTC"""
+        result = parse_timezone_data('UTC')
+        assert isinstance(result, ZoneInfo)
+        assert str(result) == 'UTC'
+
+    def test_parse_timezone_data_empty_string(self):
+        """Test parse_timezone_data with empty string falls back to system timezone"""
+        result = parse_timezone_data('')
+        assert isinstance(result, ZoneInfo)
+
+    def test_parse_timezone_data_invalid_timezone(self):
+        """Test parse_timezone_data with invalid timezone falls back to system timezone"""
+        # Invalid timezones fall back to system timezone or UTC
+        result = parse_timezone_data('Invalid/Timezone')
+        assert isinstance(result, ZoneInfo)
+        # Should be either system timezone or UTC
+
+    def test_parse_timezone_data_none(self):
+        """Test parse_timezone_data with None falls back to system timezone"""
+        result = parse_timezone_data()
+        assert isinstance(result, ZoneInfo)
+
+    def test_parse_timezone_data_various_timezones(self):
+        """Test parse_timezone_data with various timezone strings"""
+        timezones = ['America/New_York', 'Europe/London', 'Asia/Seoul']
+        for tz in timezones:
+            result = parse_timezone_data(tz)
+            assert isinstance(result, ZoneInfo)
+            assert str(result) == tz
+
+
+class TestGetDatetimeIso8601:
+    """Test suite for get_datetime_iso8601 function"""
+
+    def test_get_datetime_iso8601_default_params(self):
+        """Test get_datetime_iso8601 with default parameters"""
+        result = get_datetime_iso8601()
+        # Should be in ISO 8601 format with T separator and microseconds
+        assert 'T' in result
+        assert '.' in result  # microseconds
+        # Check basic ISO 8601 format
+        datetime.fromisoformat(result)  # Should not raise
+
+    def test_get_datetime_iso8601_custom_timezone_string(self):
+        """Test get_datetime_iso8601 with custom timezone string"""
+        result = get_datetime_iso8601('UTC')
+        assert '+00:00' in result or 'Z' in result or result.endswith('+00:00')
+
+    def test_get_datetime_iso8601_custom_timezone_zoneinfo(self):
+        """Test get_datetime_iso8601 with ZoneInfo object"""
+        tz = ZoneInfo('Asia/Tokyo')
+        result = get_datetime_iso8601(tz)
+        assert 'T' in result
+        datetime.fromisoformat(result)  # Should not raise
+
+    def test_get_datetime_iso8601_custom_separator(self):
+        """Test get_datetime_iso8601 with custom separator"""
+        result = get_datetime_iso8601(sep=' ')
+        assert ' ' in result
+        assert 'T' not in result
+
+    def test_get_datetime_iso8601_different_timespec(self):
+        """Test get_datetime_iso8601 with different timespec values"""
+        result_seconds = get_datetime_iso8601(timespec='seconds')
+        assert '.' not in result_seconds  # No microseconds
+
+        result_milliseconds = get_datetime_iso8601(timespec='milliseconds')
+        # Should have milliseconds (3 digits after decimal)
+        assert '.' in result_milliseconds
+
+
+class TestValidateDate:
+    """Test suite for validate_date function"""
+
+    def test_validate_date_valid_hyphen_format(self):
+        """Test validate_date with valid Y-m-d format"""
+        assert validate_date('2023-12-25') is True
+        assert validate_date('2024-01-01') is True
+
+    def test_validate_date_valid_slash_format(self):
+        """Test validate_date with valid Y/m/d format"""
+        assert validate_date('2023/12/25') is True
+        assert validate_date('2024/01/01') is True
+
+    def test_validate_date_invalid_format(self):
+        """Test validate_date with invalid format"""
+        assert validate_date('25-12-2023') is False
+        assert validate_date('2023.12.25') is False
+        assert validate_date('invalid') is False
+
+    def test_validate_date_invalid_date(self):
+        """Test validate_date with invalid date values"""
+        assert validate_date('2023-13-01') is False  # Invalid month
+        assert validate_date('2023-02-30') is False  # Invalid day
+
+    def test_validate_date_with_not_before(self):
+        """Test validate_date with not_before constraint"""
+        not_before = datetime(2023, 12, 1)
+        assert validate_date('2023-12-25', not_before=not_before) is True
+        assert validate_date('2023-11-25', not_before=not_before) is False
+
+    def test_validate_date_with_not_after(self):
+        """Test validate_date with not_after constraint"""
+        not_after = datetime(2023, 12, 31)
+        assert validate_date('2023-12-25', not_after=not_after) is True
+        assert validate_date('2024-01-01', not_after=not_after) is False
+
+    def test_validate_date_with_both_constraints(self):
+        """Test validate_date with both not_before and not_after constraints"""
+        not_before = datetime(2023, 12, 1)
+        not_after = datetime(2023, 12, 31)
+        assert validate_date('2023-12-15', not_before=not_before, not_after=not_after) is True
+        assert validate_date('2023-11-30', not_before=not_before, not_after=not_after) is False
+        assert validate_date('2024-01-01', not_before=not_before, not_after=not_after) is False
+
+
+class TestParseFlexibleDate:
+    """Test suite for parse_flexible_date function"""
+
+    def test_parse_flexible_date_iso8601_full(self):
+        """Test parse_flexible_date with full ISO 8601 format"""
+        result = parse_flexible_date('2023-12-25T15:30:45')
+        assert isinstance(result, datetime)
+        assert result.year == 2023
+        assert result.month == 12
+        assert result.day == 25
+        assert result.hour == 15
+        assert result.minute == 30
+        assert result.second == 45
+
+    def test_parse_flexible_date_iso8601_with_microseconds(self):
+        """Test parse_flexible_date with microseconds"""
+        result = parse_flexible_date('2023-12-25T15:30:45.123456')
+        assert isinstance(result, datetime)
+        assert result.microsecond == 123456
+
+    def test_parse_flexible_date_simple_date(self):
+        """Test parse_flexible_date with simple date format"""
+        result = parse_flexible_date('2023-12-25')
+        assert isinstance(result, datetime)
+        assert result.year == 2023
+        assert result.month == 12
+        assert result.day == 25
+
+    def test_parse_flexible_date_with_timezone_string(self):
+        """Test parse_flexible_date with timezone string"""
+        result = parse_flexible_date('2023-12-25T15:30:45', timezone_tz='Asia/Tokyo')
+        assert isinstance(result, datetime)
+        assert result.tzinfo is not None
+
+    def test_parse_flexible_date_with_timezone_zoneinfo(self):
+        """Test parse_flexible_date with ZoneInfo object"""
+        tz = ZoneInfo('UTC')
+        result = parse_flexible_date('2023-12-25T15:30:45', timezone_tz=tz)
+        assert isinstance(result, datetime)
+        assert result.tzinfo is not None
+
+    def test_parse_flexible_date_with_timezone_no_shift(self):
+        """Test parse_flexible_date with timezone but no shift"""
+        result = parse_flexible_date('2023-12-25T15:30:45', timezone_tz='UTC', shift_time_zone=False)
+        assert isinstance(result, datetime)
+        assert result.hour == 15  # Should not shift
+
+    def test_parse_flexible_date_with_timezone_shift(self):
+        """Test parse_flexible_date with timezone shift"""
+        result = parse_flexible_date('2023-12-25T15:30:45+00:00', timezone_tz='Asia/Tokyo', shift_time_zone=True)
+        assert isinstance(result, datetime)
+        assert result.tzinfo is not None
+
+    def test_parse_flexible_date_invalid_format(self):
+        """Test parse_flexible_date with invalid format returns None"""
+        result = parse_flexible_date('invalid-date')
+        assert result is None
+
+    def test_parse_flexible_date_whitespace(self):
+        """Test parse_flexible_date with whitespace"""
+        result = parse_flexible_date('  2023-12-25  ')
+        assert isinstance(result, datetime)
+        assert result.year == 2023
+
+
+class TestCompareDates:
+    """Test suite for compare_dates function"""
+
+    def test_compare_dates_first_newer(self):
+        """Test compare_dates when first date is newer"""
+        result = compare_dates('2024-01-02', '2024-01-01')
+        assert result is True
+
+    def test_compare_dates_first_older(self):
+        """Test compare_dates when first date is older"""
+        result = compare_dates('2024-01-01', '2024-01-02')
+        assert result is False
+
+    def test_compare_dates_equal(self):
+        """Test compare_dates when dates are equal"""
+        result = compare_dates('2024-01-01', '2024-01-01')
+        assert result is False
+
+    def test_compare_dates_with_time(self):
+        """Test compare_dates with time components (should only compare dates)"""
+        result = compare_dates('2024-01-02T10:00:00', '2024-01-01T23:59:59')
+        assert result is True
+
+    def test_compare_dates_invalid_first_date(self):
+        """Test compare_dates with invalid first date"""
+        result = compare_dates('invalid', '2024-01-01')
+        assert result is None
+
+    def test_compare_dates_invalid_second_date(self):
+        """Test compare_dates with invalid second date"""
+        result = compare_dates('2024-01-01', 'invalid')
+        assert result is None
+
+    def test_compare_dates_both_invalid(self):
+        """Test compare_dates with both dates invalid"""
+        result = compare_dates('invalid1', 'invalid2')
+        assert result is None
+
+
+class TestFindNewestDatetimeInList:
+    """Test suite for find_newest_datetime_in_list function"""
+
+    def test_find_newest_datetime_in_list_basic(self):
+        """Test find_newest_datetime_in_list with basic list"""
+        dates = [
+            '2023-12-25T10:00:00',
+            '2024-01-01T12:00:00',
+            '2023-11-15T08:00:00'
+        ]
+        result = find_newest_datetime_in_list(dates)
+        assert result == '2024-01-01T12:00:00'
+
+    def test_find_newest_datetime_in_list_with_timezone(self):
+        """Test find_newest_datetime_in_list with timezone-aware dates"""
+        dates = [
+            '2025-08-06T16:17:39.747+09:00',
+            '2025-08-05T16:17:39.747+09:00',
+            '2025-08-07T16:17:39.747+09:00'
+        ]
+        result = find_newest_datetime_in_list(dates)
+        assert result == '2025-08-07T16:17:39.747+09:00'
+
+    def test_find_newest_datetime_in_list_empty_list(self):
+        """Test find_newest_datetime_in_list with empty list"""
+        result = find_newest_datetime_in_list([])
+        assert result is None
+
+    def test_find_newest_datetime_in_list_single_date(self):
+        """Test find_newest_datetime_in_list with single date"""
+        dates = ['2024-01-01T12:00:00']
+        result = find_newest_datetime_in_list(dates)
+        assert result == '2024-01-01T12:00:00'
+
+    def test_find_newest_datetime_in_list_with_invalid_dates(self):
+        """Test find_newest_datetime_in_list with some invalid dates"""
+        dates = [
+            '2023-12-25T10:00:00',
+            'invalid-date',
+            '2024-01-01T12:00:00'
+        ]
+        result = find_newest_datetime_in_list(dates)
+        assert result == '2024-01-01T12:00:00'
+
+    def test_find_newest_datetime_in_list_all_invalid(self):
+        """Test find_newest_datetime_in_list with all invalid dates"""
+        dates = ['invalid1', 'invalid2', 'invalid3']
+        result = find_newest_datetime_in_list(dates)
+        assert result is None
+
+    def test_find_newest_datetime_in_list_mixed_formats(self):
+        """Test find_newest_datetime_in_list with mixed date formats"""
+        dates = [
+            '2023-12-25',
+            '2024-01-01T12:00:00',
+            '2023-11-15T08:00:00.123456'
+        ]
+        result = find_newest_datetime_in_list(dates)
+        assert result == '2024-01-01T12:00:00'
+
+
+class TestParseDayOfWeekRange:
+    """Test suite for parse_day_of_week_range function"""
+
+    def test_parse_day_of_week_range_single_day(self):
+        """Test parse_day_of_week_range with single day"""
+        result = parse_day_of_week_range('Mon')
+        assert result == [(1, 'Mon')]
+
+    def test_parse_day_of_week_range_multiple_days(self):
+        """Test parse_day_of_week_range with multiple days"""
+        result = parse_day_of_week_range('Mon,Wed,Fri')
+        assert len(result) == 3
+        assert (1, 'Mon') in result
+        assert (3, 'Wed') in result
+        assert (5, 'Fri') in result
+
+    def test_parse_day_of_week_range_simple_range(self):
+        """Test parse_day_of_week_range with simple range"""
+        result = parse_day_of_week_range('Mon-Fri')
+        assert len(result) == 5
+        assert result[0] == (1, 'Mon')
+        assert result[-1] == (5, 'Fri')
+
+    def test_parse_day_of_week_range_weekend_spanning(self):
+        """Test parse_day_of_week_range with weekend-spanning range"""
+        result = parse_day_of_week_range('Fri-Mon')
+        assert len(result) == 4
+        assert (5, 'Fri') in result
+        assert (6, 'Sat') in result
+        assert (7, 'Sun') in result
+        assert (1, 'Mon') in result
+
+    def test_parse_day_of_week_range_long_names(self):
+        """Test parse_day_of_week_range with long day names - only works in ranges"""
+        # Long names only work in ranges, not as standalone days
+        # This is a limitation of the current implementation
+        with pytest.raises(ValueError) as exc_info:
+            parse_day_of_week_range('Monday,Wednesday')
+        assert 'Invalid day of week entry found' in str(exc_info.value)
+
+    def test_parse_day_of_week_range_mixed_format(self):
+        """Test parse_day_of_week_range with short names and ranges"""
+        result = parse_day_of_week_range('Mon,Wed-Fri')
+        assert len(result) == 4
+        assert (1, 'Mon') in result
+        assert (3, 'Wed') in result
+        assert (4, 'Thu') in result
+        assert (5, 'Fri') in result
+
+    def test_parse_day_of_week_range_invalid_day(self):
+        """Test parse_day_of_week_range with invalid day"""
+        with pytest.raises(ValueError) as exc_info:
+            parse_day_of_week_range('InvalidDay')
+        assert 'Invalid day of week entry found' in str(exc_info.value)
+
+    def test_parse_day_of_week_range_duplicate_days(self):
+        """Test parse_day_of_week_range with duplicate days"""
+        with pytest.raises(ValueError) as exc_info:
+            parse_day_of_week_range('Mon,Mon')
+        assert 'Duplicate day of week entries found' in str(exc_info.value)
+
+    def test_parse_day_of_week_range_whitespace_handling(self):
+        """Test parse_day_of_week_range with extra whitespace"""
+        result = parse_day_of_week_range(' Mon , Wed , Fri ')
+        assert len(result) == 3
+        assert (1, 'Mon') in result
+
+
+class TestParseTimeRange:
+    """Test suite for parse_time_range function"""
+
+    def test_parse_time_range_valid(self):
+        """Test parse_time_range with valid time range"""
+        start, end = parse_time_range('09:00-17:00')
+        assert start == time(9, 0)
+        assert end == time(17, 0)
+
+    def test_parse_time_range_different_times(self):
+        """Test parse_time_range with different time values"""
+        start, end = parse_time_range('08:30-12:45')
+        assert start == time(8, 30)
+        assert end == time(12, 45)
+
+    def test_parse_time_range_invalid_block(self):
+        """Test parse_time_range with invalid block format"""
+        with pytest.raises(ValueError) as exc_info:
+            parse_time_range('09:00')
+        assert 'Invalid time block' in str(exc_info.value)
+
+    def test_parse_time_range_invalid_format(self):
+        """Test parse_time_range with invalid time format"""
+        with pytest.raises(ValueError) as exc_info:
+            parse_time_range('25:00-26:00')
+        assert 'Invalid time block format' in str(exc_info.value)
+
+    def test_parse_time_range_start_after_end(self):
+        """Test parse_time_range with start time after end time"""
+        with pytest.raises(ValueError) as exc_info:
+            parse_time_range('17:00-09:00')
+        assert 'start time after end time' in str(exc_info.value)
+
+    def test_parse_time_range_equal_times(self):
+        """Test parse_time_range with equal start and end times"""
+        with pytest.raises(ValueError) as exc_info:
+            parse_time_range('09:00-09:00')
+        assert 'start time after end time or equal' in str(exc_info.value)
+
+    def test_parse_time_range_custom_format(self):
+        """Test parse_time_range with custom time format"""
+        start, end = parse_time_range('09:00:00-17:00:00', time_format='%H:%M:%S')
+        assert start == time(9, 0, 0)
+        assert end == time(17, 0, 0)
+
+    def test_parse_time_range_whitespace(self):
+        """Test parse_time_range with whitespace"""
+        start, end = parse_time_range('  09:00-17:00  ')
+        assert start == time(9, 0)
+        assert end == time(17, 0)
+
+
+class TestTimesOverlapOrConnect:
+    """Test suite for times_overlap_or_connect function"""
+
+    def test_times_overlap_or_connect_clear_overlap(self):
+        """Test times_overlap_or_connect with clear overlap"""
+        time1 = (time(9, 0), time(12, 0))
+        time2 = (time(10, 0), time(14, 0))
+        assert times_overlap_or_connect(time1, time2) is True
+
+    def test_times_overlap_or_connect_no_overlap(self):
+        """Test times_overlap_or_connect with no overlap"""
+        time1 = (time(9, 0), time(12, 0))
+        time2 = (time(13, 0), time(17, 0))
+        assert times_overlap_or_connect(time1, time2) is False
+
+    def test_times_overlap_or_connect_touching_not_allowed(self):
+        """Test times_overlap_or_connect with touching ranges (not allowed)"""
+        time1 = (time(8, 0), time(10, 0))
+        time2 = (time(10, 0), time(12, 0))
+        assert times_overlap_or_connect(time1, time2, allow_touching=False) is True
+
+    def test_times_overlap_or_connect_touching_allowed(self):
+        """Test times_overlap_or_connect with touching ranges (allowed)"""
+        time1 = (time(8, 0), time(10, 0))
+        time2 = (time(10, 0), time(12, 0))
+        assert times_overlap_or_connect(time1, time2, allow_touching=True) is False
+
+    def test_times_overlap_or_connect_one_contains_other(self):
+        """Test times_overlap_or_connect when one range contains the other"""
+        time1 = (time(9, 0), time(17, 0))
+        time2 = (time(10, 0), time(12, 0))
+        assert times_overlap_or_connect(time1, time2) is True
+
+    def test_times_overlap_or_connect_same_start(self):
+        """Test times_overlap_or_connect with same start time"""
+        time1 = (time(9, 0), time(12, 0))
+        time2 = (time(9, 0), time(14, 0))
+        assert times_overlap_or_connect(time1, time2) is True
+
+    def test_times_overlap_or_connect_same_end(self):
+        """Test times_overlap_or_connect with same end time"""
+        time1 = (time(9, 0), time(12, 0))
+        time2 = (time(10, 0), time(12, 0))
+        assert times_overlap_or_connect(time1, time2) is True
+
+
+class TestIsTimeInRange:
+    """Test suite for is_time_in_range function"""
+
+    def test_is_time_in_range_within_range(self):
+        """Test is_time_in_range with time within range"""
+        assert is_time_in_range('10:00:00', '09:00:00', '17:00:00') is True
+
+    def test_is_time_in_range_at_start(self):
+        """Test is_time_in_range with time at start of range"""
+        assert is_time_in_range('09:00:00', '09:00:00', '17:00:00') is True
+
+    def test_is_time_in_range_at_end(self):
+        """Test is_time_in_range with time at end of range"""
+        assert is_time_in_range('17:00:00', '09:00:00', '17:00:00') is True
+
+    def test_is_time_in_range_before_range(self):
+        """Test is_time_in_range with time before range"""
+        assert is_time_in_range('08:00:00', '09:00:00', '17:00:00') is False
+
+    def test_is_time_in_range_after_range(self):
+        """Test is_time_in_range with time after range"""
+        assert is_time_in_range('18:00:00', '09:00:00', '17:00:00') is False
+
+    def test_is_time_in_range_crosses_midnight(self):
+        """Test is_time_in_range with range crossing midnight"""
+        # Range from 22:00 to 06:00
+        assert is_time_in_range('23:00:00', '22:00:00', '06:00:00') is True
+        assert is_time_in_range('03:00:00', '22:00:00', '06:00:00') is True
+        assert is_time_in_range('12:00:00', '22:00:00', '06:00:00') is False
+
+    def test_is_time_in_range_midnight_boundary(self):
+        """Test is_time_in_range at midnight"""
+        assert is_time_in_range('00:00:00', '22:00:00', '06:00:00') is True
+
+
+class TestReorderWeekdaysFromToday:
+    """Test suite for reorder_weekdays_from_today function"""
+
+    def test_reorder_weekdays_from_monday(self):
+        """Test reorder_weekdays_from_today starting from Monday"""
+        result = reorder_weekdays_from_today('Mon')
+        values = list(result.values())
+        assert values[0] == 'Mon'
+        assert values[-1] == 'Sun'
+        assert len(result) == 7
+
+    def test_reorder_weekdays_from_wednesday(self):
+        """Test reorder_weekdays_from_today starting from Wednesday"""
+        result = reorder_weekdays_from_today('Wed')
+        values = list(result.values())
+        assert values[0] == 'Wed'
+        assert values[1] == 'Thu'
+        assert values[-1] == 'Tue'
+
+    def test_reorder_weekdays_from_sunday(self):
+        """Test reorder_weekdays_from_today starting from Sunday"""
+        result = reorder_weekdays_from_today('Sun')
+        values = list(result.values())
+        assert values[0] == 'Sun'
+        assert values[-1] == 'Sat'
+
+    def test_reorder_weekdays_from_long_name(self):
+        """Test reorder_weekdays_from_today with long day name"""
+        result = reorder_weekdays_from_today('Friday')
+        values = list(result.values())
+        assert values[0] == 'Fri'
+        assert values[-1] == 'Thu'
+
+    def test_reorder_weekdays_invalid_day(self):
+        """Test reorder_weekdays_from_today with invalid day name"""
+        with pytest.raises(ValueError) as exc_info:
+            reorder_weekdays_from_today('InvalidDay')
+        assert 'Invalid day name provided' in str(exc_info.value)
+
+    def test_reorder_weekdays_preserves_all_days(self):
+        """Test that reorder_weekdays_from_today preserves all 7 days"""
+        for day in ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']:
+            result = reorder_weekdays_from_today(day)
+            assert len(result) == 7
+            assert set(result.values()) == {'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'}
+
+
+class TestEdgeCases:
+    """Test suite for edge cases and integration scenarios"""
+
+    def test_parse_flexible_date_with_various_iso_formats(self):
+        """Test parse_flexible_date handles various ISO format variations"""
+        formats = [
+            '2023-12-25',
+            '2023-12-25T15:30:45',
+            '2023-12-25T15:30:45.123456',
+        ]
+        for date_str in formats:
+            result = parse_flexible_date(date_str)
+            assert result is not None
+            assert isinstance(result, datetime)
+
+    def test_timezone_consistency_across_functions(self):
+        """Test timezone handling consistency across functions"""
+        tz_str = 'Asia/Tokyo'
+        tz_obj = parse_timezone_data(tz_str)
+        
+        # Both should work with get_datetime_iso8601
+        result1 = get_datetime_iso8601(tz_str)
+        result2 = get_datetime_iso8601(tz_obj)
+        
+        assert result1 is not None
+        assert result2 is not None
+
+    def test_date_validation_and_parsing_consistency(self):
+        """Test that validate_date and parse_flexible_date agree"""
+        valid_dates = ['2023-12-25', '2024/01/01']
+        for date_str in valid_dates:
+            # normalize format for parse_flexible_date
+            normalized = date_str.replace('/', '-')
+            assert validate_date(date_str) is True
+            assert parse_flexible_date(normalized) is not None
+
+    def test_day_of_week_range_complex_scenario(self):
+        """Test parse_day_of_week_range with complex mixed input"""
+        result = parse_day_of_week_range('Mon,Wed-Fri,Sun')
+        assert len(result) == 5
+        assert (1, 'Mon') in result
+        assert (3, 'Wed') in result
+        assert (4, 'Thu') in result
+        assert (5, 'Fri') in result
+        assert (7, 'Sun') in result
+
+    def test_time_range_boundary_conditions(self):
+        """Test parse_time_range with boundary times"""
+        start, end = parse_time_range('00:00-23:59')
+        assert start == time(0, 0)
+        assert end == time(23, 59)
+
+# __END__
diff --git a/tests/unit/datetime_handling/test_seconds_to_string.py b/tests/unit/datetime_handling/test_seconds_to_string.py
new file mode 100644
index 0000000..7402ad1
--- /dev/null
+++ b/tests/unit/datetime_handling/test_seconds_to_string.py
@@ -0,0 +1,462 @@
+"""
+PyTest: datetime_handling/timestamp_convert - seconds_to_string and convert_timestamp functions
+"""
+
+from corelibs.datetime_handling.timestamp_convert import seconds_to_string, convert_timestamp
+
+
+class TestSecondsToString:
+    """Test suite for seconds_to_string function"""
+
+    def test_basic_integer_seconds(self):
+        """Test conversion of basic integer seconds"""
+        assert seconds_to_string(0) == "0s"
+        assert seconds_to_string(1) == "1s"
+        assert seconds_to_string(30) == "30s"
+        assert seconds_to_string(59) == "59s"
+
+    def test_minutes_conversion(self):
+        """Test conversion involving minutes"""
+        assert seconds_to_string(60) == "1m"
+        assert seconds_to_string(90) == "1m 30s"
+        assert seconds_to_string(120) == "2m"
+        assert seconds_to_string(3599) == "59m 59s"
+
+    def test_hours_conversion(self):
+        """Test conversion involving hours"""
+        assert seconds_to_string(3600) == "1h"
+        assert seconds_to_string(3660) == "1h 1m"
+        assert seconds_to_string(3661) == "1h 1m 1s"
+        assert seconds_to_string(7200) == "2h"
+        assert seconds_to_string(7260) == "2h 1m"
+
+    def test_days_conversion(self):
+        """Test conversion involving days"""
+        assert seconds_to_string(86400) == "1d"
+        assert seconds_to_string(86401) == "1d 1s"
+        assert seconds_to_string(90000) == "1d 1h"
+        assert seconds_to_string(90061) == "1d 1h 1m 1s"
+        assert seconds_to_string(172800) == "2d"
+
+    def test_complex_combinations(self):
+        """Test complex time combinations"""
+        # 1 day, 2 hours, 3 minutes, 4 seconds
+        total = 86400 + 7200 + 180 + 4
+        assert seconds_to_string(total) == "1d 2h 3m 4s"
+
+        # 5 days, 23 hours, 59 minutes, 59 seconds
+        total = 5 * 86400 + 23 * 3600 + 59 * 60 + 59
+        assert seconds_to_string(total) == "5d 23h 59m 59s"
+
+    def test_fractional_seconds_default_precision(self):
+        """Test fractional seconds with default precision (3 decimal places)"""
+        assert seconds_to_string(0.1) == "0.1s"
+        assert seconds_to_string(0.123) == "0.123s"
+        assert seconds_to_string(0.1234) == "0.123s"
+        assert seconds_to_string(1.5) == "1.5s"
+        assert seconds_to_string(1.567) == "1.567s"
+        assert seconds_to_string(1.5678) == "1.568s"
+
+    def test_fractional_seconds_microsecond_precision(self):
+        """Test fractional seconds with microsecond precision"""
+        assert seconds_to_string(0.1, show_microseconds=True) == "0.1s"
+        assert seconds_to_string(0.123456, show_microseconds=True) == "0.123456s"
+        assert seconds_to_string(0.1234567, show_microseconds=True) == "0.123457s"
+        assert seconds_to_string(1.5, show_microseconds=True) == "1.5s"
+        assert seconds_to_string(1.567890, show_microseconds=True) == "1.56789s"
+
+    def test_fractional_seconds_with_larger_units(self):
+        """Test fractional seconds combined with larger time units"""
+        # 1 minute and 30.5 seconds
+        assert seconds_to_string(90.5) == "1m 30.5s"
+        assert seconds_to_string(90.5, show_microseconds=True) == "1m 30.5s"
+
+        # 1 hour, 1 minute, and 1.123 seconds
+        total = 3600 + 60 + 1.123
+        assert seconds_to_string(total) == "1h 1m 1.123s"
+        assert seconds_to_string(total, show_microseconds=True) == "1h 1m 1.123s"
+
+    def test_negative_values(self):
+        """Test negative time values"""
+        assert seconds_to_string(-1) == "-1s"
+        assert seconds_to_string(-60) == "-1m"
+        assert seconds_to_string(-90) == "-1m 30s"
+        assert seconds_to_string(-3661) == "-1h 1m 1s"
+        assert seconds_to_string(-86401) == "-1d 1s"
+        assert seconds_to_string(-1.5) == "-1.5s"
+        assert seconds_to_string(-90.123) == "-1m 30.123s"
+
+    def test_zero_handling(self):
+        """Test various zero values"""
+        assert seconds_to_string(0) == "0s"
+        assert seconds_to_string(0.0) == "0s"
+        assert seconds_to_string(-0) == "0s"
+        assert seconds_to_string(-0.0) == "0s"
+
+    def test_float_input_types(self):
+        """Test various float input types"""
+        assert seconds_to_string(1.0) == "1s"
+        assert seconds_to_string(60.0) == "1m"
+        assert seconds_to_string(3600.0) == "1h"
+        assert seconds_to_string(86400.0) == "1d"
+
+    def test_large_values(self):
+        """Test handling of large time values"""
+        # 365 days (1 year)
+        year_seconds = 365 * 86400
+        assert seconds_to_string(year_seconds) == "365d"
+
+        # 1000 days
+        assert seconds_to_string(1000 * 86400) == "1000d"
+
+        # Large number with all units
+        large_time = 999 * 86400 + 23 * 3600 + 59 * 60 + 59.999
+        result = seconds_to_string(large_time)
+        assert result.startswith("999d")
+        assert "23h" in result
+        assert "59m" in result
+        assert "59.999s" in result
+
+    def test_rounding_behavior(self):
+        """Test rounding behavior for fractional seconds"""
+        # Default precision (3 decimal places) - values are truncated via rstrip
+        assert seconds_to_string(1.0004) == "1s"  # Truncates trailing zeros after rstrip
+        assert seconds_to_string(1.0005) == "1s"  # Truncates trailing zeros after rstrip
+        assert seconds_to_string(1.9999) == "2s"  # Rounds up and strips .000
+
+        # Microsecond precision (6 decimal places)
+        assert seconds_to_string(1.0000004, show_microseconds=True) == "1s"
+        assert seconds_to_string(1.0000005, show_microseconds=True) == "1.000001s"
+
+    def test_trailing_zero_removal(self):
+        """Test that trailing zeros are properly removed"""
+        assert seconds_to_string(1.100) == "1.1s"
+        assert seconds_to_string(1.120) == "1.12s"
+        assert seconds_to_string(1.123) == "1.123s"
+        assert seconds_to_string(1.100000, show_microseconds=True) == "1.1s"
+        assert seconds_to_string(1.123000, show_microseconds=True) == "1.123s"
+
+    def test_invalid_input_types(self):
+        """Test handling of invalid input types"""
+        # String inputs should be returned as-is
+        assert seconds_to_string("invalid") == "invalid"
+        assert seconds_to_string("not a number") == "not a number"
+        assert seconds_to_string("") == ""
+
+    def test_edge_cases_boundary_values(self):
+        """Test edge cases at unit boundaries"""
+        # Exactly 1 minute - 1 second
+        assert seconds_to_string(59) == "59s"
+        assert seconds_to_string(59.999) == "59.999s"
+
+        # Exactly 1 hour - 1 second
+        assert seconds_to_string(3599) == "59m 59s"
+        assert seconds_to_string(3599.999) == "59m 59.999s"
+
+        # Exactly 1 day - 1 second
+        assert seconds_to_string(86399) == "23h 59m 59s"
+        assert seconds_to_string(86399.999) == "23h 59m 59.999s"
+
+    def test_very_small_fractional_seconds(self):
+        """Test very small fractional values"""
+        assert seconds_to_string(0.001) == "0.001s"
+        assert seconds_to_string(0.0001) == "0s"  # Below default precision
+        assert seconds_to_string(0.000001, show_microseconds=True) == "0.000001s"
+        assert seconds_to_string(0.0000001, show_microseconds=True) == "0s"  # Below microsecond precision
+
+    def test_precision_consistency(self):
+        """Test that precision is consistent across different scenarios"""
+        # With other units present
+        assert seconds_to_string(61.123456) == "1m 1.123s"
+        assert seconds_to_string(61.123456, show_microseconds=True) == "1m 1.123456s"
+
+        # Large values with fractional seconds
+        large_val = 90061.123456  # 1d 1h 1m 1.123456s
+        assert seconds_to_string(large_val) == "1d 1h 1m 1.123s"
+        assert seconds_to_string(large_val, show_microseconds=True) == "1d 1h 1m 1.123456s"
+
+    def test_string_numeric_inputs(self):
+        """Test string inputs that represent numbers"""
+        # String inputs should be returned as-is, even if they look like numbers
+        assert seconds_to_string("60") == "60"
+        assert seconds_to_string("1.5") == "1.5"
+        assert seconds_to_string("0") == "0"
+        assert seconds_to_string("-60") == "-60"
+
+
+class TestConvertTimestamp:
+    """Test suite for convert_timestamp function"""
+
+    def test_basic_integer_seconds(self):
+        """Test conversion of basic integer seconds"""
+        assert convert_timestamp(0) == "0s 0ms"
+        assert convert_timestamp(1) == "1s 0ms"
+        assert convert_timestamp(30) == "30s 0ms"
+        assert convert_timestamp(59) == "59s 0ms"
+
+    def test_basic_without_microseconds(self):
+        """Test conversion without showing microseconds"""
+        assert convert_timestamp(0, show_microseconds=False) == "0s"
+        assert convert_timestamp(1, show_microseconds=False) == "1s"
+        assert convert_timestamp(30, show_microseconds=False) == "30s"
+        assert convert_timestamp(59, show_microseconds=False) == "59s"
+
+    def test_minutes_conversion(self):
+        """Test conversion involving minutes"""
+        assert convert_timestamp(60) == "1m 0s 0ms"
+        assert convert_timestamp(90) == "1m 30s 0ms"
+        assert convert_timestamp(120) == "2m 0s 0ms"
+        assert convert_timestamp(3599) == "59m 59s 0ms"
+
+    def test_minutes_conversion_without_microseconds(self):
+        """Test conversion involving minutes without microseconds"""
+        assert convert_timestamp(60, show_microseconds=False) == "1m 0s"
+        assert convert_timestamp(90, show_microseconds=False) == "1m 30s"
+        assert convert_timestamp(120, show_microseconds=False) == "2m 0s"
+
+    def test_hours_conversion(self):
+        """Test conversion involving hours"""
+        assert convert_timestamp(3600) == "1h 0m 0s 0ms"
+        assert convert_timestamp(3660) == "1h 1m 0s 0ms"
+        assert convert_timestamp(3661) == "1h 1m 1s 0ms"
+        assert convert_timestamp(7200) == "2h 0m 0s 0ms"
+        assert convert_timestamp(7260) == "2h 1m 0s 0ms"
+
+    def test_hours_conversion_without_microseconds(self):
+        """Test conversion involving hours without microseconds"""
+        assert convert_timestamp(3600, show_microseconds=False) == "1h 0m 0s"
+        assert convert_timestamp(3660, show_microseconds=False) == "1h 1m 0s"
+        assert convert_timestamp(3661, show_microseconds=False) == "1h 1m 1s"
+
+    def test_days_conversion(self):
+        """Test conversion involving days"""
+        assert convert_timestamp(86400) == "1d 0h 0m 0s 0ms"
+        assert convert_timestamp(86401) == "1d 0h 0m 1s 0ms"
+        assert convert_timestamp(90000) == "1d 1h 0m 0s 0ms"
+        assert convert_timestamp(90061) == "1d 1h 1m 1s 0ms"
+        assert convert_timestamp(172800) == "2d 0h 0m 0s 0ms"
+
+    def test_days_conversion_without_microseconds(self):
+        """Test conversion involving days without microseconds"""
+        assert convert_timestamp(86400, show_microseconds=False) == "1d 0h 0m 0s"
+        assert convert_timestamp(86401, show_microseconds=False) == "1d 0h 0m 1s"
+        assert convert_timestamp(90000, show_microseconds=False) == "1d 1h 0m 0s"
+
+    def test_complex_combinations(self):
+        """Test complex time combinations"""
+        # 1 day, 2 hours, 3 minutes, 4 seconds
+        total = 86400 + 7200 + 180 + 4
+        assert convert_timestamp(total) == "1d 2h 3m 4s 0ms"
+
+        # 5 days, 23 hours, 59 minutes, 59 seconds
+        total = 5 * 86400 + 23 * 3600 + 59 * 60 + 59
+        assert convert_timestamp(total) == "5d 23h 59m 59s 0ms"
+
+    def test_fractional_seconds_with_microseconds(self):
+        """Test fractional seconds showing microseconds"""
+        # Note: ms value is the integer of the decimal part string after rounding to 4 places
+        assert convert_timestamp(0.1) == "0s 1ms"  # 0.1 → "0.1" → ms=1
+        assert convert_timestamp(0.123) == "0s 123ms"  # 0.123 → "0.123" → ms=123
+        assert convert_timestamp(0.1234) == "0s 1234ms"  # 0.1234 → "0.1234" → ms=1234
+        assert convert_timestamp(1.5) == "1s 5ms"  # 1.5 → "1.5" → ms=5
+        assert convert_timestamp(1.567) == "1s 567ms"  # 1.567 → "1.567" → ms=567
+        assert convert_timestamp(1.5678) == "1s 5678ms"  # 1.5678 rounds to 1.5678 → ms=5678
+
+    def test_fractional_seconds_rounding(self):
+        """Test rounding of fractional seconds to 4 decimal places"""
+        # The function rounds to 4 decimal places before splitting
+        assert convert_timestamp(0.12345) == "0s 1235ms"  # Rounds to 0.1235
+        assert convert_timestamp(0.123456) == "0s 1235ms"  # Rounds to 0.1235
+        assert convert_timestamp(1.99999) == "2s 0ms"  # Rounds to 2.0
+
+    def test_fractional_seconds_with_larger_units(self):
+        """Test fractional seconds combined with larger time units"""
+        # 1 minute and 30.5 seconds
+        assert convert_timestamp(90.5) == "1m 30s 5ms"
+
+        # 1 hour, 1 minute, and 1.123 seconds
+        total = 3600 + 60 + 1.123
+        assert convert_timestamp(total) == "1h 1m 1s 123ms"
+
+    def test_negative_values(self):
+        """Test negative time values"""
+        assert convert_timestamp(-1) == "-1s 0ms"
+        assert convert_timestamp(-60) == "-1m 0s 0ms"
+        assert convert_timestamp(-90) == "-1m 30s 0ms"
+        assert convert_timestamp(-3661) == "-1h 1m 1s 0ms"
+        assert convert_timestamp(-86401) == "-1d 0h 0m 1s 0ms"
+        assert convert_timestamp(-1.5) == "-1s 5ms"
+        assert convert_timestamp(-90.123) == "-1m 30s 123ms"
+
+    def test_negative_without_microseconds(self):
+        """Test negative values without microseconds"""
+        assert convert_timestamp(-1, show_microseconds=False) == "-1s"
+        assert convert_timestamp(-60, show_microseconds=False) == "-1m 0s"
+        assert convert_timestamp(-90.123, show_microseconds=False) == "-1m 30s"
+
+    def test_zero_handling(self):
+        """Test various zero values"""
+        assert convert_timestamp(0) == "0s 0ms"
+        assert convert_timestamp(0.0) == "0s 0ms"
+        assert convert_timestamp(-0) == "0s 0ms"
+        assert convert_timestamp(-0.0) == "0s 0ms"
+
+    def test_zero_filling_behavior(self):
+        """Test that zeros are filled between set values"""
+        # If we have days and seconds, hours and minutes should be 0
+        assert convert_timestamp(86401) == "1d 0h 0m 1s 0ms"
+
+        # If we have hours and seconds, minutes should be 0
+        assert convert_timestamp(3601) == "1h 0m 1s 0ms"
+
+        # If we have days and hours, minutes and seconds should be 0
+        assert convert_timestamp(90000) == "1d 1h 0m 0s 0ms"
+
+    def test_milliseconds_display(self):
+        """Test milliseconds are always shown when show_microseconds=True"""
+        # Even with no fractional part, 0ms should be shown
+        assert convert_timestamp(1) == "1s 0ms"
+        assert convert_timestamp(60) == "1m 0s 0ms"
+        assert convert_timestamp(3600) == "1h 0m 0s 0ms"
+
+        # With fractional part, ms should be shown
+        assert convert_timestamp(1.001) == "1s 1ms"  # "1.001" → ms=1
+        assert convert_timestamp(1.0001) == "1s 1ms"  # "1.0001" → ms=1
+
+    def test_float_input_types(self):
+        """Test various float input types"""
+        assert convert_timestamp(1.0) == "1s 0ms"
+        assert convert_timestamp(60.0) == "1m 0s 0ms"
+        assert convert_timestamp(3600.0) == "1h 0m 0s 0ms"
+        assert convert_timestamp(86400.0) == "1d 0h 0m 0s 0ms"
+
+    def test_large_values(self):
+        """Test handling of large time values"""
+        # 365 days (1 year)
+        year_seconds = 365 * 86400
+        assert convert_timestamp(year_seconds) == "365d 0h 0m 0s 0ms"
+
+        # 1000 days
+        assert convert_timestamp(1000 * 86400) == "1000d 0h 0m 0s 0ms"
+
+        # Large number with all units
+        large_time = 999 * 86400 + 23 * 3600 + 59 * 60 + 59.999
+        result = convert_timestamp(large_time)
+        assert result.startswith("999d")
+        assert "23h" in result
+        assert "59m" in result
+        assert "59s" in result
+        assert "999ms" in result  # 59.999 rounds to 59.999, ms=999
+
+    def test_invalid_input_types(self):
+        """Test handling of invalid input types"""
+        # String inputs should be returned as-is
+        assert convert_timestamp("invalid") == "invalid"
+        assert convert_timestamp("not a number") == "not a number"
+        assert convert_timestamp("") == ""
+
+    def test_string_numeric_inputs(self):
+        """Test string inputs that represent numbers"""
+        # String inputs should be returned as-is, even if they look like numbers
+        assert convert_timestamp("60") == "60"
+        assert convert_timestamp("1.5") == "1.5"
+        assert convert_timestamp("0") == "0"
+        assert convert_timestamp("-60") == "-60"
+
+    def test_edge_cases_boundary_values(self):
+        """Test edge cases at unit boundaries"""
+        # Exactly 1 minute - 1 second
+        assert convert_timestamp(59) == "59s 0ms"
+        assert convert_timestamp(59.999) == "59s 999ms"
+
+        # Exactly 1 hour - 1 second
+        assert convert_timestamp(3599) == "59m 59s 0ms"
+        assert convert_timestamp(3599.999) == "59m 59s 999ms"
+
+        # Exactly 1 day - 1 second
+        assert convert_timestamp(86399) == "23h 59m 59s 0ms"
+        assert convert_timestamp(86399.999) == "23h 59m 59s 999ms"
+
+    def test_very_small_fractional_seconds(self):
+        """Test very small fractional values"""
+        assert convert_timestamp(0.001) == "0s 1ms"  # 0.001 → "0.001" → ms=1
+        assert convert_timestamp(0.0001) == "0s 1ms"  # 0.0001 → "0.0001" → ms=1
+        assert convert_timestamp(0.00005) == "0s 1ms"  # 0.00005 rounds to 0.0001 → ms=1
+        assert convert_timestamp(0.00004) == "0s 0ms"  # 0.00004 rounds to 0.0 → ms=0
+
+    def test_milliseconds_extraction(self):
+        """Test that milliseconds are correctly extracted from fractional part"""
+        # The ms value is the integer of the decimal part string, not a conversion
+        # So 0.1 → "0.1" → ms=1, NOT 100ms as you might expect
+        assert convert_timestamp(0.1) == "0s 1ms"
+        # 0.01 seconds → "0.01" → ms=1 (int("01") = 1)
+        assert convert_timestamp(0.01) == "0s 1ms"
+        # 0.001 seconds → "0.001" → ms=1
+        assert convert_timestamp(0.001) == "0s 1ms"
+        # 0.0001 seconds → "0.0001" → ms=1
+        assert convert_timestamp(0.0001) == "0s 1ms"
+        # 0.00004 seconds rounds to "0.0" → ms=0
+        assert convert_timestamp(0.00004) == "0s 0ms"
+
+    def test_comparison_with_seconds_to_string(self):
+        """Test differences between convert_timestamp and seconds_to_string"""
+        # convert_timestamp fills zeros and adds ms
+        # seconds_to_string omits zeros and no ms
+        assert convert_timestamp(86401) == "1d 0h 0m 1s 0ms"
+        assert seconds_to_string(86401) == "1d 1s"
+
+        assert convert_timestamp(3661) == "1h 1m 1s 0ms"
+        assert seconds_to_string(3661) == "1h 1m 1s"
+
+        # With microseconds disabled, still different due to zero-filling
+        assert convert_timestamp(86401, show_microseconds=False) == "1d 0h 0m 1s"
+        assert seconds_to_string(86401) == "1d 1s"
+
+    def test_precision_consistency(self):
+        """Test that precision is consistent across different scenarios"""
+        # With other units present
+        assert convert_timestamp(61.123456) == "1m 1s 1235ms"  # Rounds to 61.1235
+
+        # Large values with fractional seconds
+        large_val = 90061.123456  # 1d 1h 1m 1.123456s
+        assert convert_timestamp(large_val) == "1d 1h 1m 1s 1235ms"  # Rounds to .1235
+
+    def test_microseconds_flag_consistency(self):
+        """Test that show_microseconds flag works consistently"""
+        test_values = [0, 1, 60, 3600, 86400, 1.5, 90.123, -60]
+
+        for val in test_values:
+            with_ms = convert_timestamp(val, show_microseconds=True)
+            without_ms = convert_timestamp(val, show_microseconds=False)
+
+            # With microseconds should contain 'ms', without should not
+            assert "ms" in with_ms
+            assert "ms" not in without_ms
+
+            # Both should start with same sign if negative
+            if val < 0:
+                assert with_ms.startswith("-")
+                assert without_ms.startswith("-")
+
+    def test_format_consistency(self):
+        """Test that output format is consistent"""
+        # All outputs should have consistent spacing and unit ordering
+        # Format should be: [d ]h m s[ ms]
+        result = convert_timestamp(93784.5678)  # 1d 2h 3m 4.5678s
+        # 93784.5678 rounds to 93784.5678, splits to ["93784", "5678"]
+        assert result == "1d 2h 3m 4s 5678ms"
+
+        # Verify parts are in correct order
+        parts = result.split()
+        # Extract units properly: last 1-2 chars that are letters
+        units = []
+        for p in parts:
+            if p.endswith('ms'):
+                units.append('ms')
+            elif p[-1].isalpha():
+                units.append(p[-1])
+        # Should be in order: d, h, m, s, ms
+        expected_order = ['d', 'h', 'm', 's', 'ms']
+        assert units == expected_order
+
+# __END__
diff --git a/tests/unit/string_handling/test_timestamp_strings.py b/tests/unit/datetime_handling/test_timestamp_strings.py
similarity index 84%
rename from tests/unit/string_handling/test_timestamp_strings.py
rename to tests/unit/datetime_handling/test_timestamp_strings.py
index ebfabb9..be025e5 100644
--- a/tests/unit/string_handling/test_timestamp_strings.py
+++ b/tests/unit/datetime_handling/test_timestamp_strings.py
@@ -1,5 +1,5 @@
 """
-PyTest: string_handling/timestamp_strings
+PyTest: datetime_handling/timestamp_strings
 """
 
 from datetime import datetime
@@ -8,7 +8,7 @@ from zoneinfo import ZoneInfo
 import pytest
 
 # Assuming the class is in a file called timestamp_strings.py
-from corelibs.string_handling.timestamp_strings import TimestampStrings
+from corelibs.datetime_handling.timestamp_strings import TimestampStrings
 
 
 class TestTimestampStrings:
@@ -16,7 +16,7 @@ class TestTimestampStrings:
 
     def test_default_initialization(self):
         """Test initialization with default timezone"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 15, 30, 45)
             mock_datetime.now.return_value = mock_now
 
@@ -32,7 +32,7 @@ class TestTimestampStrings:
         """Test initialization with custom timezone"""
         custom_tz = 'America/New_York'
 
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 15, 30, 45)
             mock_datetime.now.return_value = mock_now
 
@@ -52,7 +52,7 @@ class TestTimestampStrings:
 
     def test_timestamp_formats(self):
         """Test various timestamp format outputs"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             # Mock both datetime.now() calls
             mock_now = datetime(2023, 12, 25, 9, 5, 3)
             mock_now_tz = datetime(2023, 12, 25, 23, 5, 3, tzinfo=ZoneInfo('Asia/Tokyo'))
@@ -68,7 +68,7 @@ class TestTimestampStrings:
 
     def test_different_timezones_produce_different_results(self):
         """Test that different timezones produce different timestamp_tz values"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 12, 0, 0)
             mock_datetime.now.return_value = mock_now
 
@@ -86,7 +86,7 @@ class TestTimestampStrings:
 
     def test_none_timezone_uses_default(self):
         """Test that passing None for timezone uses class default"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 15, 30, 45)
             mock_datetime.now.return_value = mock_now
 
@@ -96,7 +96,7 @@ class TestTimestampStrings:
 
     def test_timestamp_file_format_no_colons(self):
         """Test that timestamp_file format doesn't contain colons (safe for filenames)"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 15, 30, 45)
             mock_datetime.now.return_value = mock_now
 
@@ -108,7 +108,7 @@ class TestTimestampStrings:
 
     def test_multiple_instances_independent(self):
         """Test that multiple instances don't interfere with each other"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 15, 30, 45)
             mock_datetime.now.return_value = mock_now
 
@@ -121,8 +121,8 @@ class TestTimestampStrings:
 
     def test_zoneinfo_called_correctly_with_string(self):
         """Test that ZoneInfo is called with correct timezone when passing string"""
-        with patch('corelibs.string_handling.timestamp_strings.ZoneInfo') as mock_zoneinfo:
-            with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.ZoneInfo') as mock_zoneinfo:
+            with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
                 mock_now = datetime(2023, 12, 25, 15, 30, 45)
                 mock_datetime.now.return_value = mock_now
 
@@ -134,7 +134,7 @@ class TestTimestampStrings:
 
     def test_zoneinfo_object_parameter(self):
         """Test that ZoneInfo objects can be passed directly as timezone parameter"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 15, 30, 45)
             mock_now_tz = datetime(2023, 12, 25, 15, 30, 45, tzinfo=ZoneInfo('Europe/Paris'))
             mock_datetime.now.side_effect = [mock_now, mock_now_tz]
@@ -149,7 +149,7 @@ class TestTimestampStrings:
 
     def test_zoneinfo_object_vs_string_equivalence(self):
         """Test that ZoneInfo object and string produce equivalent results"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 15, 30, 45)
             mock_now_tz = datetime(2023, 12, 25, 15, 30, 45, tzinfo=ZoneInfo('Europe/Paris'))
             mock_datetime.now.side_effect = [mock_now, mock_now_tz, mock_now, mock_now_tz]
@@ -171,7 +171,7 @@ class TestTimestampStrings:
 
     def test_edge_case_midnight(self):
         """Test timestamp formatting at midnight"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2023, 12, 25, 0, 0, 0)
             mock_datetime.now.return_value = mock_now
 
@@ -182,7 +182,7 @@ class TestTimestampStrings:
 
     def test_edge_case_new_year(self):
         """Test timestamp formatting at new year"""
-        with patch('corelibs.string_handling.timestamp_strings.datetime') as mock_datetime:
+        with patch('corelibs.datetime_handling.timestamp_strings.datetime') as mock_datetime:
             mock_now = datetime(2024, 1, 1, 0, 0, 0)
             mock_datetime.now.return_value = mock_now
 
diff --git a/tests/unit/string_handling/test_seconds_to_string.py b/tests/unit/string_handling/test_seconds_to_string.py
deleted file mode 100644
index 2645c18..0000000
--- a/tests/unit/string_handling/test_seconds_to_string.py
+++ /dev/null
@@ -1,186 +0,0 @@
-"""
-PyTest: string_handling/timestamp_strings - seconds_to_string function
-"""
-
-from corelibs.string_handling.timestamp_strings import seconds_to_string
-
-
-class TestSecondsToString:
-    """Test suite for seconds_to_string function"""
-
-    def test_basic_integer_seconds(self):
-        """Test conversion of basic integer seconds"""
-        assert seconds_to_string(0) == "0s"
-        assert seconds_to_string(1) == "1s"
-        assert seconds_to_string(30) == "30s"
-        assert seconds_to_string(59) == "59s"
-
-    def test_minutes_conversion(self):
-        """Test conversion involving minutes"""
-        assert seconds_to_string(60) == "1m"
-        assert seconds_to_string(90) == "1m 30s"
-        assert seconds_to_string(120) == "2m"
-        assert seconds_to_string(3599) == "59m 59s"
-
-    def test_hours_conversion(self):
-        """Test conversion involving hours"""
-        assert seconds_to_string(3600) == "1h"
-        assert seconds_to_string(3660) == "1h 1m"
-        assert seconds_to_string(3661) == "1h 1m 1s"
-        assert seconds_to_string(7200) == "2h"
-        assert seconds_to_string(7260) == "2h 1m"
-
-    def test_days_conversion(self):
-        """Test conversion involving days"""
-        assert seconds_to_string(86400) == "1d"
-        assert seconds_to_string(86401) == "1d 1s"
-        assert seconds_to_string(90000) == "1d 1h"
-        assert seconds_to_string(90061) == "1d 1h 1m 1s"
-        assert seconds_to_string(172800) == "2d"
-
-    def test_complex_combinations(self):
-        """Test complex time combinations"""
-        # 1 day, 2 hours, 3 minutes, 4 seconds
-        total = 86400 + 7200 + 180 + 4
-        assert seconds_to_string(total) == "1d 2h 3m 4s"
-
-        # 5 days, 23 hours, 59 minutes, 59 seconds
-        total = 5 * 86400 + 23 * 3600 + 59 * 60 + 59
-        assert seconds_to_string(total) == "5d 23h 59m 59s"
-
-    def test_fractional_seconds_default_precision(self):
-        """Test fractional seconds with default precision (3 decimal places)"""
-        assert seconds_to_string(0.1) == "0.1s"
-        assert seconds_to_string(0.123) == "0.123s"
-        assert seconds_to_string(0.1234) == "0.123s"
-        assert seconds_to_string(1.5) == "1.5s"
-        assert seconds_to_string(1.567) == "1.567s"
-        assert seconds_to_string(1.5678) == "1.568s"
-
-    def test_fractional_seconds_microsecond_precision(self):
-        """Test fractional seconds with microsecond precision"""
-        assert seconds_to_string(0.1, show_microseconds=True) == "0.1s"
-        assert seconds_to_string(0.123456, show_microseconds=True) == "0.123456s"
-        assert seconds_to_string(0.1234567, show_microseconds=True) == "0.123457s"
-        assert seconds_to_string(1.5, show_microseconds=True) == "1.5s"
-        assert seconds_to_string(1.567890, show_microseconds=True) == "1.56789s"
-
-    def test_fractional_seconds_with_larger_units(self):
-        """Test fractional seconds combined with larger time units"""
-        # 1 minute and 30.5 seconds
-        assert seconds_to_string(90.5) == "1m 30.5s"
-        assert seconds_to_string(90.5, show_microseconds=True) == "1m 30.5s"
-
-        # 1 hour, 1 minute, and 1.123 seconds
-        total = 3600 + 60 + 1.123
-        assert seconds_to_string(total) == "1h 1m 1.123s"
-        assert seconds_to_string(total, show_microseconds=True) == "1h 1m 1.123s"
-
-    def test_negative_values(self):
-        """Test negative time values"""
-        assert seconds_to_string(-1) == "-1s"
-        assert seconds_to_string(-60) == "-1m"
-        assert seconds_to_string(-90) == "-1m 30s"
-        assert seconds_to_string(-3661) == "-1h 1m 1s"
-        assert seconds_to_string(-86401) == "-1d 1s"
-        assert seconds_to_string(-1.5) == "-1.5s"
-        assert seconds_to_string(-90.123) == "-1m 30.123s"
-
-    def test_zero_handling(self):
-        """Test various zero values"""
-        assert seconds_to_string(0) == "0s"
-        assert seconds_to_string(0.0) == "0s"
-        assert seconds_to_string(-0) == "0s"
-        assert seconds_to_string(-0.0) == "0s"
-
-    def test_float_input_types(self):
-        """Test various float input types"""
-        assert seconds_to_string(1.0) == "1s"
-        assert seconds_to_string(60.0) == "1m"
-        assert seconds_to_string(3600.0) == "1h"
-        assert seconds_to_string(86400.0) == "1d"
-
-    def test_large_values(self):
-        """Test handling of large time values"""
-        # 365 days (1 year)
-        year_seconds = 365 * 86400
-        assert seconds_to_string(year_seconds) == "365d"
-
-        # 1000 days
-        assert seconds_to_string(1000 * 86400) == "1000d"
-
-        # Large number with all units
-        large_time = 999 * 86400 + 23 * 3600 + 59 * 60 + 59.999
-        result = seconds_to_string(large_time)
-        assert result.startswith("999d")
-        assert "23h" in result
-        assert "59m" in result
-        assert "59.999s" in result
-
-    def test_rounding_behavior(self):
-        """Test rounding behavior for fractional seconds"""
-        # Default precision (3 decimal places) - values are truncated via rstrip
-        assert seconds_to_string(1.0004) == "1s"  # Truncates trailing zeros after rstrip
-        assert seconds_to_string(1.0005) == "1s"  # Truncates trailing zeros after rstrip
-        assert seconds_to_string(1.9999) == "2s"  # Rounds up and strips .000
-
-        # Microsecond precision (6 decimal places)
-        assert seconds_to_string(1.0000004, show_microseconds=True) == "1s"
-        assert seconds_to_string(1.0000005, show_microseconds=True) == "1.000001s"
-
-    def test_trailing_zero_removal(self):
-        """Test that trailing zeros are properly removed"""
-        assert seconds_to_string(1.100) == "1.1s"
-        assert seconds_to_string(1.120) == "1.12s"
-        assert seconds_to_string(1.123) == "1.123s"
-        assert seconds_to_string(1.100000, show_microseconds=True) == "1.1s"
-        assert seconds_to_string(1.123000, show_microseconds=True) == "1.123s"
-
-    def test_invalid_input_types(self):
-        """Test handling of invalid input types"""
-        # String inputs should be returned as-is
-        assert seconds_to_string("invalid") == "invalid"
-        assert seconds_to_string("not a number") == "not a number"
-        assert seconds_to_string("") == ""
-
-    def test_edge_cases_boundary_values(self):
-        """Test edge cases at unit boundaries"""
-        # Exactly 1 minute - 1 second
-        assert seconds_to_string(59) == "59s"
-        assert seconds_to_string(59.999) == "59.999s"
-
-        # Exactly 1 hour - 1 second
-        assert seconds_to_string(3599) == "59m 59s"
-        assert seconds_to_string(3599.999) == "59m 59.999s"
-
-        # Exactly 1 day - 1 second
-        assert seconds_to_string(86399) == "23h 59m 59s"
-        assert seconds_to_string(86399.999) == "23h 59m 59.999s"
-
-    def test_very_small_fractional_seconds(self):
-        """Test very small fractional values"""
-        assert seconds_to_string(0.001) == "0.001s"
-        assert seconds_to_string(0.0001) == "0s"  # Below default precision
-        assert seconds_to_string(0.000001, show_microseconds=True) == "0.000001s"
-        assert seconds_to_string(0.0000001, show_microseconds=True) == "0s"  # Below microsecond precision
-
-    def test_precision_consistency(self):
-        """Test that precision is consistent across different scenarios"""
-        # With other units present
-        assert seconds_to_string(61.123456) == "1m 1.123s"
-        assert seconds_to_string(61.123456, show_microseconds=True) == "1m 1.123456s"
-
-        # Large values with fractional seconds
-        large_val = 90061.123456  # 1d 1h 1m 1.123456s
-        assert seconds_to_string(large_val) == "1d 1h 1m 1.123s"
-        assert seconds_to_string(large_val, show_microseconds=True) == "1d 1h 1m 1.123456s"
-
-    def test_string_numeric_inputs(self):
-        """Test string inputs that represent numbers"""
-        # String inputs should be returned as-is, even if they look like numbers
-        assert seconds_to_string("60") == "60"
-        assert seconds_to_string("1.5") == "1.5"
-        assert seconds_to_string("0") == "0"
-        assert seconds_to_string("-60") == "-60"
-
-# __END__
diff --git a/tests/unit/string_handling/test_var_helpers.py b/tests/unit/var_handling/test_var_helpers.py
similarity index 100%
rename from tests/unit/string_handling/test_var_helpers.py
rename to tests/unit/var_handling/test_var_helpers.py