feat(pytest): use commandOverride for RunTests and DiscoverTest

[gnufede]

What

PyTest.RunTests and DiscoverTests hardcoded python -m pytest, ignoring the commandOverride loaded from --command or DD_TEST_OPTIMIZATION_RUNNER_COMMAND. This PR makes them use commandOverride when set, so callers can run pytest (the console script) instead of python -m pytest.

Why

python -m pytest sets sys.argv[0] to pytest's __main__.py, which ddtrace's detect_service incorrectly treats as a test file path → service='pytest' instead of the module name (e.g. 'tests.contrib.graphql'). pytest (console script) sets argv[0]='pytest' which detect_service skips → correct service inference.

This is needed for the dd-trace-py ddtest dogfooding: ddtest runs python -m pytest by default, which breaks snapshot tests. With this change, dd-trace-py sets DD_TEST_OPTIMIZATION_RUNNER_COMMAND=pytest and ddtest runs pytest <files> instead.

How to test

DD_TEST_OPTIMIZATION_RUNNER_COMMAND=pytest ./bin/ddtest run -p python -f pytest --ci-node 0 → sys.argv[0]='pytest' → detect_service skips it → correct module name.

Two new tests:

• TestPyTest_RunTests_WithCommandOverride: verifies RunTests uses commandOverride
• TestPyTest_DiscoverTests_WithCommandOverride: verifies DiscoverTests uses commandOverride

[datadog-prod-us1-3]

 

✅ All CI checks and tests passed.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 86.47% (+0.01%)

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[datadog-prod-us1-3]

A multi-part PyTest command override can share argument storage across parallel workers. Workers can replace each other's test file lists, so some tests can run twice while other tests do not run.

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[datadog-prod-us1-3]

Parallel workers share override argument storage

Some tests can run twice while other tests do not run.

Assertion details

• Input: Use parallel workers with a multi-part override such as uv run pytest when the override slice has spare capacity.
• Expected: Each worker must use a private argument slice. Clone the override arguments in RunTests before append. Apply the same safe handling in DiscoverTests, and add a multi-part parallel override test.
• Actual: args shares the command-override backing array. Concurrent workers append different test files to this shared storage and can replace each other's arguments.

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