Add tests for require-virtualenv

As far as I know, the require-virtualenv functionality is essentially entirely untested. This is the main reason why it is not documented (see also https://github.com/pypa/pip/issues/2429).

It would be good to see tests for --require-virtualenv

Functional tests that verify it actually works (who knows, perhaps our virtual environment detection logic will break in some weird edge case down the road)
Unit/functional tests that force us to explicitly decide whether a new command should opt-in or opt-out of the --require-virtualenv feature

Below, I've attached some old discussion on this topic.

It would be nice to have a test for this - but I note that #8603 didn't include a test, so I'm inclined to accept this without a test and add tests for both cases in a follow-up PR.

I started taking a look at the tests- as far as I can tell require_venv isn't actually tested anywhere and it's not clear to me that there would be any benefit to testing the behavior of ignore_require_venv for this particular command.

This is the only reference I can find (tests/unit/test_options.py) and it only seems to be asserting that the order (command, option) doesn't matter.

480     def test_require_virtualenv(self) -> None:
481         # FakeCommand intentionally returns the wrong type.
482         options1, args1 = cast(
483             Tuple[Values, List[str]], main(["--require-virtualenv", "fake"])
484         )
485         options2, args2 = cast(
486             Tuple[Values, List[str]], main(["fake", "--require-virtualenv"])
487         )
488         assert options1.require_venv
489         assert options2.require_venv

my first thought is to implement something like:

mock virtualenv by monkey patching running_under_virtualenv() in cli/base_command.py (with return value of has_venv column in table below)
mock ignore_require_venv by monkeypatching FakeCommand
test condition:
- if require_venv and not ignore_require_venv and not has_venv: assert_option_error(msg)

however... that test condition looks an awful lot like a reimplementation of the original implementation...

# cli/base_command.py
        if options.require_venv and not self.ignore_require_venv:
            # If a venv is required check if it can really be found
            if not running_under_virtualenv():
                logger.critical("Could not find an activated virtualenv (required).")
                sys.exit(VIRTUALENV_NOT_FOUND)

error condition truth matrix:

"has_venv"	"require_venv"	"ignore_require_venv"	"should_error"
T	T	T	F
T	T	F	F
T	F	T	F
T	F	F	F
F	T	T	F
F	T	F	T
F	F	T	F

so I guess I'm a little lost on what a test for this should look like...

Originally posted by @justin-f-perez in https://github.com/pypa/pip/issues/10658#issuecomment-968286761

For the erroring case, could we avoid the monkey patching and just define a custom command and 'pretend' we're not in a virtualenv, something like (the attribute setting/restoring magic should probably be in a fixture/context manager):

    def test_require_virtualenv_errors_when_not_in_venv(self) -> None:
        class Cmd(Command):
            ignore_require_venv: bool = False

        # edit variable set by PEP-405 compliant virtualenvs
        # to pretend we're not in a venv even if we actually are
        has_base_prefix = hasattr(sys, "base_prefix")
        old_base_prefix = getattr(sys, "base_prefix", None)
        if has_base_prefix:
            delattr(sys, "base_prefix")

        try:
            with pytest.raises(SystemExit) as excinfo:
                Cmd(name="fake", summary="").main(["--require-virtualenv"])

            assert excinfo.value.code == VIRTUALENV_NOT_FOUND
        finally:
            # restore our modifications
            if has_base_prefix:
                sys.base_prefix = old_base_prefix

pypa / pip

Add tests for require-virtualenv #12843