The modern virtual environment structure does not allow us to enable
"fake user site" while disabling the global site, so we need to do more
fine-grained configuration to correctly set up test environments for
each test case.
With this done, we can also properly support the stdlib venv ad the test
environment backend, since it basically works identically with modern
virtualenv. The incompatible_with_test_venv is thus removed.
Our isolation logic for venv isn't correct and that is causing these
tests to fail. The culprits for this are:
tests/lib/venv.py::VirtualEnvironment.user_site_packages
tests/lib/venv.py::VirtualEnvironment.sitecustomize
Both these together are supposed to create an environment to isolate the
tests. However, they were written for virtualenv and make assumptions
that are not true for environments created with venv. Until we can fix
VirtualEnvironment to properly isolate the test from the underlying test
environment when using venv, these tests will continue to fail.
This is blocking an important bugfix for users facing issues with since
pip is installing packages into `--user` when run in a venv, even when
`--user` isn't visible from that environment.
As a temporary band-aid for this problem, I'm skipping these tests to
unblock us from shipping the bugfix for the aforementioned issue.
The test isolation logic should be fixed to work for venv. Once such a
fix is made, this commit should be reverted.
- cleanup virtualenv creation code
- ensure all testing virtual environments use a recent version
of setuptools / wheel, making it easier to switch to custom
versions of those, as well as reducing network accesses
- reduce size of testing virtual environment, slightly speeding
up the testsuite
