pytest - add suite name to junit.xml report

[vinnybod]

The junit.xml files generated by pytest use the name pytest by default. For any tools that consume the xml files like IDEs or CI system UIs, this makes the output unfriendly because every test case rolls up the the same test suite named pytest.

The changes here add the BAZEL_TARGET name to the suite using standard pytest command line args.

Here is an example before and after when running the tests with and without the change in IntelliJ. The example only runs two test targets. The issue becomes more apparent as the number of targets scales up.

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Changes are visible to end-users: yes/no

• Searched for relevant documentation and updated as needed: no
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

Run a py_test target that uses py_pytest_main and observe the test suite name.

[fzakaria]

This has been a great QoL improvement for us; highly recommend the merge.