[Data] Make test_hanging_detector_detects_issues more robust

[bveeramani]

Why are these changes needed?

test_hanging_detector_detects_issues checks that Ray Data emits a log if one task takes a lot longer than the others. The issue is that the test doesn't capture the log output correctly, and so the test fails even though Ray data correctly emits the log.

To make this test more robust, this PR uses pytest's caplog fixture to capture the logs rather than a bespoke custom handler.

[2025-10-08T09:00:41Z] >           assert hanging_detected, log_output
  | [2025-10-08T09:00:41Z] E           AssertionError:
  | [2025-10-08T09:00:41Z] E           assert False
  | [2025-10-08T09:00:41Z]
  | [2025-10-08T09:00:41Z] python/ray/data/tests/test_issue_detection_manager.py:153: AssertionError
  |  

Related issue number

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run pre-commit jobs to lint the changes in this PR. (pre-commit setup)
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[gemini-code-assist]

Code Review

This pull request significantly improves the robustness of test_hanging_detector_detects_issues by replacing a complex, custom log-capturing mechanism with the standard pytest caplog fixture. This change simplifies the test, makes it easier to understand, and less prone to errors. The addition of the restore_data_context fixture is also a great improvement for test isolation.

I have one suggestion to make the test assertion even more specific and robust.

[omatthew98]

Thanks!