Fix CrontabSchedule task run before schedule time

[WeJie]

This fix cater the scenairo that crontab tasks(run at every fixed time) with last_run_at is None and start_time is not None run before the scheduled time.

Fix for #912

Unit test included.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.21%. Comparing base (0bac717) to head (88c166f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #913      +/-   ##
==========================================
+ Coverage   88.19%   88.21%   +0.02%     
==========================================
  Files          32       32              
  Lines        1008     1010       +2     
  Branches      105      106       +1     
==========================================
+ Hits          889      891       +2     
  Misses        101      101              
  Partials       18       18              

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[auvipy]

@alirafiei75 would you mind having a look when available again?

[Copilot]

Pull Request Overview

This PR ensures crontab tasks with a defined start_time do not run before that time by adjusting last_run_at and adding unit tests to cover the scenario.

• Added tests to verify crontab schedules respect start_time before becoming due.
• Updated ModelEntry initialization to set last_run_at to start_time for crontab schedules.
• Enhanced tick-based tests to confirm the scheduler heap is not blocked by tasks before their start_time.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
t/unit/test_schedulers.py	New tests covering crontab start_time behavior and heap ordering
django_celery_beat/schedulers.py	Scheduler logic updated to use start_time for crontab entries, preventing early runs

[Copilot]

Using time.sleep in tests can slow down the suite and introduce flakiness; consider simulating time progression by mocking time.monotonic or the scheduler’s time source instead.

Suggested change

	time.sleep(3)
	s.tick()
	with patch('time.monotonic', side_effect=lambda: monotonic() + 3):
	s.tick()

[Copilot]

Patching time.monotonic this way may lead to recursion if monotonic refers to the patched function; patch the scheduler module’s reference or call the original time.monotonic inside the side effect to avoid infinite recursion.

Suggested change

	with patch('time.monotonic', side_effect=lambda: monotonic() + 54):
	original_monotonic = time.monotonic
	with patch('time.monotonic', side_effect=lambda: original_monotonic() + 54):

[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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[Copilot]

[nitpick] The condition logic is hard to read with the line break and negation. Consider refactoring to improve clarity, such as checking for crontab first or using a more descriptive variable.

Suggested change

	if isinstance(model.schedule, schedules.schedule) \
	and not isinstance(model.schedule, schedules.crontab):
	is_interval_schedule = (
	isinstance(model.schedule, schedules.schedule)
	and not isinstance(model.schedule, schedules.crontab)
	)
	if is_interval_schedule:

[cclauss]

Suggested change

	if isinstance(model.schedule, schedules.schedule) \
	and not isinstance(model.schedule, schedules.crontab):
	if isinstance(model.schedule, (schedules.crontab, schedules.schedule)):

% ruff rule PIE810 # Shorter, faster, easier to understand/

• https://docs.astral.sh/ruff/rules/multiple-starts-ends-with

[cclauss]

PEP8 suggests avoiding backslashes in Python code because whitespace to the right of the backslash breaks the code on a change that is invisible to the reader. Put the contents on a single line and then allow ruff format or psf/black to reformat the code.