[testing, CI] fix coverage statistics issue caused by test_common.py tracer patching

[icfaust]

Description

Python code coverage has been introduced in #2222 and #2225. Some code, while properly covered with tests, was showing incorrect coverage. It was discovered that the tracing used in test_common.py interferes with the tracing collected by pytest-cov. Any tests alphabetically after test_common.py have been neglected in codecov and by coverage.py. Correcting this can be done by tracing the estimators in a separate process and passing the data back to the pytest-cov parent process.

This has been implemented using python multiprocessing due to the time overhead of loading sklearnex for each estimator and method. The process persists for the period of all test_common.py tests as a daemon process. The test passing/xfail/etc rate has been verified to match to main.

No performance metrics are generated due to purely for testing and CI.

The effectiveness of this change can be observed by the ~1.2% improvement in code coverage (as indirect changes).

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Flag	Coverage Δ
github	84.39% <ø> (+1.20%)	⬆️

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see 13 files with indirect coverage changes

[icfaust]

/intelci: run

[icfaust]

/intelci: run

[ethanglaser]

Is 1.2% increase what you would expect? In general, where does the other missing coverage come from?

[icfaust]

Is 1.2% increase what you would expect? In general, where does the other missing coverage come from?

@ethanglaser good question! Its mainly 2 aspects: 1) The utils/validation.py tests coverage was not being recorded, 2) centralized testing (especially test_patching.py) was not being recorded, which covers all other methods of estimators (especially score) which otherwise might not be specifically tested in the individual estimator tests. With the fix these are now recorded, and that means these tests provide an additional 1.2% of the codebase coverage not seen in sklearn conformance or estimator/onedal tests.