The top-level directories in a wheel are packages, so this means they all clobber the top-level tests package name. If the wheel contains a "test" package, it even clobbers the "test" package from the standard library (which contains tests for Python itself, the built-in testing package is "unittest").

I think that's just a misconfiguration due to the relatively common layout of

  - .git
  - pyproject.toml / setup.py / setup.cfg etc.
  - src/mypackage
  - tests/test_module1.py
  - tests/test_module2.py

Depending on how you configure stuff you might accidentally include the tests directory as a separate top-level package next to all packages under "src". If you stick to the legacy ways, this does not happen if you just used the usual

    setup(
        ...,
        packages=find_packages('src'),
        package_dir={'': 'src'},
    )

I think this is the default behavior of setuptools nowadays if you do not say anything at all in any of the config files about where your code is.

If you actually intend to ship the tests, because they don't require a specialized environment to run, then the project layout should really be

  - .git
  - pyproject.toml / setup.py / setup.cfg etc.
  - src/mypackage
  - src/mypackage/tests/test_module1.py

Downstream consumers who might want to ship this as part of something larger should ideally be able to just delete mypackage/tests without anything breaking.