pip_cert fixture breaks tests if PIP_CERT is in os.environ

[frenzymadness]

The new fixture pip_cert implemented in bc787b2 does not work if PIP_CERT is in os.environ. Pytest expect it to yield a value because it's recognized as a generator but if PIP_CERT is present in os.environ, the fixture returns None which causes pytest to fail with:

fixturefunc = <function pip_cert at 0x7f14f12ef3a0>
request = <SubRequest 'pip_cert' for <Function test_python[no_prompt]>>
kwargs = {'tmp_path_factory': TempPathFactory(_given_basetemp=None, _trace=<pluggy._tracing.TagTracerSub object at 0x7f14f0197490>, _basetemp=PosixPath('/tmp/pytest-of-mockbuild/pytest-0'))}

    def call_fixture_func(
        fixturefunc: "_FixtureFunc[_FixtureValue]", request: FixtureRequest, kwargs
    ) -> _FixtureValue:
        if is_generator(fixturefunc):
            fixturefunc = cast(
                Callable[..., Generator[_FixtureValue, None, None]], fixturefunc
            )
            generator = fixturefunc(**kwargs)
            try:
                fixture_result = next(generator)
            except StopIteration:
>               raise ValueError(
                    "{} did not yield a value".format(request.fixturename)
                ) from None
E               ValueError: pip_cert did not yield a value

fixturefunc = <function pip_cert at 0x7f14f12ef3a0>
generator  = <generator object pip_cert at 0x7f14ed790580>
kwargs     = {'tmp_path_factory': TempPathFactory(_given_basetemp=None, _trace=<pluggy._tracing.TagTracerSub object at 0x7f14f0197490>, _basetemp=PosixPath('/tmp/pytest-of-mockbuild/pytest-0'))}
request    = <SubRequest 'pip_cert' for <Function test_python[no_prompt]>>

/usr/lib/python3.9/site-packages/_pytest/fixtures.py:917: ValueError

An easy fix might be to use the condition in the decorator like @pytest.fixture(autouse=ensure_str("PIP_CERT") not in os.environ, scope="session").

[hroncok]

What about changing the return to yield and moving the rest of the function to an else branch?

virtualenv/tests/conftest.py

Lines 151 to 163 in a4025d6

	@pytest.fixture(autouse=True, scope="session")
	def pip_cert(tmp_path_factory):
	# workaround for https:/pypa/pip/issues/8984 - if the certificate is explicitly set no error can happen
	key = ensure_str("PIP_CERT")
	if key in os.environ:
	return
	cert = tmp_path_factory.mktemp("folder") / "cert"
	import pkgutil
	cert_data = pkgutil.get_data("pip._vendor.certifi", "cacert.pem")
	cert.write_bytes(cert_data)
	with change_os_environ(key, str(cert)):
	yield

@pytest.fixture(autouse=True, scope="session")
def pip_cert(tmp_path_factory):
    # workaround for https:/pypa/pip/issues/8984 - if the certificate is explicitly set no error can happen
    key = ensure_str("PIP_CERT")
    if key in os.environ:
        yield
    else:
        cert = tmp_path_factory.mktemp("folder") / "cert"
        import pkgutil

        cert_data = pkgutil.get_data("pip._vendor.certifi", "cacert.pem")
        cert.write_bytes(cert_data)
        with change_os_environ(key, str(cert)):
            yield

[frenzymadness]

Would it be helpful to prepare a PR with the proposed change?

[gaborbernat]

Yes.

[frenzymadness]

On it.