Reenable coverate instrumentation of test files

[labbati]

With this change https://github.com/DataDog/dd-trace-py/pull/11379/files#diff-3985b6c4c52757d7d726c3002c85935f582641d687acd0f6ab50f93e1294205dR330 in #11379 we had made a number of tests in tests/coverage/ failing by design, since now the coverage code was non-instrumenting code if it is vendored (aka non-user code). Tests were regularly failing in main.

Problem is that code from dd-trace-py/tests is considered vendored by the algorithm, as dd-trace-py is installed locally (think pip install -e ./) by the hatch dd_coverage.py3.* environments, used to run tests: https://gitlab.ddbuild.io/DataDog/apm-reliability/dd-trace-py/-/jobs/747303728#L56.

This commit introduces an hack: if the code is invoked as part of a pytest run AND comes from the tests folder, then can be instrumented by the coverage module.

While not proud of it, it is the best trade off I could think about without foundational changes to how we run tests in pytest.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/internal/coverage/code.py                                       @DataDog/apm-core-python @datadog/ci-app-libraries
ddtrace/internal/packages.py                                            @DataDog/apm-core-python

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-12-24 14:33:21

Comparing candidate commit 736ec99 in PR branch labbati/coverage-broken-tests with baseline commit 998ee2c in branch main.

Found 1 performance improvements and 2 performance regressions! Performance is the same for 391 metrics, 2 unstable metrics.

scenario:iast_aspects-ospathdirname_aspect

• 🟥 execution_time [+300.996ns; +367.269ns] or [+8.265%; +10.085%]

scenario:iast_aspects-ospathjoin_aspect

• 🟩 execution_time [-508.698ns; -433.617ns] or [-9.025%; -7.693%]

scenario:iast_aspects-ospathsplitdrive_aspect

• 🟥 execution_time [+190.191ns; +234.595ns] or [+7.157%; +8.829%]