[Bug] pytest-xdist workers race on captured_info.txt in patched testing utils
Author: oleksii-tumanov
Pull request: no
Labels: name: bug

### System Info

Transformers=5.6.0.dev0 (local checkout 85099df959); 
Python=3.13.5; 
Platform=macOS-26.2-arm64-arm-64bit-Mach-O; 
pytest=8.4.2; 
pytest-xdist=3.8.0

### Who can help?

@ydshieh @SunMarc 

### Information

- [ ] The official example scripts
- [ ] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction
This issue affects internal test utilities and does not involve example scripts or a user dataset/task.

1. In src/transformers/testing_utils.py, _prepare_debugging_info() appends to captured_info.txt and patch_testing_methods_to_collect_info() unlinks that same file.
2. Run tests under pytest -n 2 with workers sharing the same _PATCHED_TESTING_METHODS_OUTPUT_DIR.
3. Observe that workers write to and reset the same captured_info.txt, so one worker can delete or interleave another worker's captured debugging output.

I checked for overlapping issues and PRs and did not find a direct match. 
I have a candidate fix with focused tests on my fork here: https://github.com/oleksii-tumanov/transformers/tree/fix/testing-utils-xdist-captured-info (commit 58dcab6ae281f04fbc3a2afb7b24235795ca885a). I am opening the issue first for coordination before submitting an upstream PR.

### Expected behavior

Each xdist worker should isolate its captured debugging output instead of sharing one `captured_info.txt` file. For example, worker-specific filenames such as `captured_info_gw0.txt` and `captured_info_gw1.txt` would avoid cross-worker clobbering while preserving the current single-file behavior for non-xdist runs.

Comments:
cc @ydshieh @tarekziade (see also the PRs at #45639 and #45645, but don't be afraid to banish any slop if it's not helpful 😅 )

The changes seems sound, I will defer to @ydshieh for reviews 

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.

> This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.
> 
> Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.

I believe this is a useful small fix

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.

This is still relevant.

I opened #45639 with a focused fix for the xdist `captured_info.txt` race while preserving the existing non-xdist behavior. Happy to adjust the approach if maintainers prefer a different direction.

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.