Raise error when encountering unhandled callbacks

[meshy]

Before now, exiting transaction would run all after-commit callbacks, on the assumption that they were enqueued inside the transaction. In tests this sometimes hid order-of-execution bugs, where pre-existing unhandled after-commit callbacks would get called, but at the wrong time.

When opening a transaction, we will now check for pre-existing unhandled after-commit callbacks, and raise an error when they're found.

Fixes #31

Alternative to #87

[HamaBarhamou]

Thanks—this looks great! Two quick points:

1. CHANGELOG / naming — Since this is tests-only, I’d either explicitly note “(tests only)” in the CHANGELOG entry or rename the flag to SUBATOMIC_TEST_CATCH_UNHANDLED_AFTER_COMMIT_CALLBACKS (and similarly SUBATOMIC_TEST_RUN_AFTER_COMMIT_CALLBACKS) to avoid ambiguity.

2. Exception DX — Exposing the callables via callbacks is handy but can get noisy (closures, long reprs). Maybe keep the attribute for debugging, but tweak the exception message/__str__ to show just a count + actionable hint, e.g.
   Found 2 unhandled on_commit callbacks. Ensure they’re run before opening a transaction, or set SUBATOMIC_TEST_CATCH_UNHANDLED_AFTER_COMMIT_CALLBACKS=False to opt out in tests.

(Nit) A brief comment in _execute_on_commit_callbacks_in_tests explaining why we check both the entry state (only_in_testcase_transaction) and the exit state (_innermost_atomic_block_wraps_testcase) would help clarify the intent (avoid false positives if context changes between enter/exit).

[meshy]

1. CHANGELOG / naming — Since this is tests-only, I’d either explicitly note “(tests only)” in the CHANGELOG entry or rename the flag to SUBATOMIC_TEST_CATCH_UNHANDLED_AFTER_COMMIT_CALLBACKS (and similarly SUBATOMIC_TEST_RUN_AFTER_COMMIT_CALLBACKS) to avoid ambiguity.

Thanks for this -- I've renamed the flag to append _IN_TESTS (which is in line with the other similar setting), and make the "in tests" nature of the change more prominent in the changelog.

2. **Exception DX** — Exposing the callables via `callbacks` is handy but can get noisy (closures, long reprs). Maybe keep the attribute for debugging, but tweak the exception message/`__str__` to show just a count + actionable hint, e.g.
   `Found 2 unhandled on_commit callbacks. Ensure they’re run before opening a transaction, or set SUBATOMIC_TEST_CATCH_UNHANDLED_AFTER_COMMIT_CALLBACKS=False to opt out in tests.`

I'm going to keep it as-is for now. While explaining the meaning of the error is likely to be useful the first time it's encountered, I think the benefit of seeing the callbacks will be most useful long-term.

(Nit) A brief comment in _execute_on_commit_callbacks_in_tests explaining why we check both the entry state (only_in_testcase_transaction) and the exit state (_innermost_atomic_block_wraps_testcase) would help clarify the intent (avoid false positives if context changes between enter/exit).

You're right, but the comments here need further improvement anyway, so I'm going to leave that for a later refinement.

[samueljsb]

One nitpick about the changelog, but otherwise this looks like it's ready now!

[samueljsb]

Nice demonstration of the cause of this problem.