$ qlist sys-apps/portage | grep test_ | grep -v pyc$ | sort /usr/lib/python3.8/site-packages/portage/tests/bin/test_dobin.py /usr/lib/python3.8/site-packages/portage/tests/bin/test_dodir.py /usr/lib/python3.8/site-packages/portage/tests/bin/test_doins.py /usr/lib/python3.8/site-packages/portage/tests/bin/test_eapi7_ver_funcs.py /usr/lib/python3.8/site-packages/portage/tests/bin/test_filter_bash_env.py ...
It's pretty common for python packages to install their test modules. Bug 366203 was about banning installation of "test" or "tests" directories at the top-level under site-packages. Portage does not do that; they are installed under the "portage" namespace. Someone might want to run the test suite from an installed copy of Portage. That is currently possible to do like so: python3.10 -m portage.tests.runTests