Isolate tests in multi_process_shared with unique temp path.

[shunping]

Flaky tests:

• https://github.com/apache/beam/actions/runs/25827712861/job/75884983570
• https://github.com/apache/beam/actions/runs/25814674014/job/75839888289

These tests were failing intermittently in parallel runs because setUp was cleaning up shared files in the default temp directory, including the ones created by any on-going tests, which interferes with concurrent tests.

This fix adds an autouse pytest fixture to force all MultiProcessShared instances to use a unique tmp_path per test, and removes the unsafe global cleanup in setUp.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses flaky tests in the multi_process_shared module by improving test isolation. By replacing shared temporary directory usage with unique paths per test and removing problematic global cleanup routines, the changes ensure that concurrent test runs do not conflict with one another.

Highlights

• Test Isolation: Introduced an autouse pytest fixture to ensure each test case uses a unique temporary directory, preventing cross-test interference.
• Cleanup Refactoring: Removed the unsafe global cleanup logic in the setUp method that was causing intermittent failures during parallel test execution.

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[gemini-code-assist]

Code Review

This pull request introduces a pytest fixture to isolate MultiProcessShared tests by injecting a unique temporary directory path during initialization, enabling safer parallel execution. It also removes manual cleanup logic from MultiProcessSharedSpawnProcessTest. Feedback was provided regarding the fragility of the mock_init implementation, specifically concerning positional arguments and explicit None values for the path parameter, with a suggestion for a more robust function signature.

[gemini-code-assist]

The current implementation of mock_init is fragile and will fail in several scenarios:

1. Positional Arguments: If path is passed as a positional argument (e.g., MultiProcessShared(cons, tag, "/path")), it will be captured in *args. Since 'path' is not in kwargs, the code will add it to kwargs, causing orig_init to receive multiple values for the path argument and raising a TypeError.
2. Explicit None: If path=None is passed explicitly as a keyword argument, the isolation will fail because 'path' in kwargs will be true, and the mock won't replace it with the unique tmp_path. The original __init__ will then fall back to the global temp directory.

A more robust approach is to explicitly capture path in the signature and check if it is None.

Suggested change

	def mock_init(self, constructor, tag, *args, **kwargs):
	if 'path' not in kwargs:
	kwargs['path'] = str(tmp_path)
	return orig_init(self, constructor, tag, *args, **kwargs)
	def mock_init(self, constructor, tag, path=None, *args, **kwargs):
	if path is None:
	path = str(tmp_path)
	return orig_init(self, constructor, tag, path, *args, **kwargs)