def pytester(
    request: FixtureRequest, tmp_path_factory: TempPathFactory, monkeypatch: MonkeyPatch
) -> Pytester:
    """
    Facilities to write tests/configuration files, execute pytest in isolation, and match
    against expected output, perfect for black-box testing of pytest plugins.

    It attempts to isolate the test run from external factors as much as possible, modifying
    the current working directory to ``path`` and environment variables during initialization.

    It is particularly useful for testing plugins. It is similar to the :fixture:`tmp_path`
    fixture but provides methods which aid in testing pytest itself.
    """
    return Pytester(request, tmp_path_factory, monkeypatch, _ispytest=True)

    Facilities to write tests/configuration files, execute pytest in isolation, and match
    against expected output, perfect for black-box testing of pytest plugins.

    It attempts to isolate the test run from external factors as much as possible, modifying
    the current working directory to ``path`` and environment variables during initialization.

    It is particularly useful for testing plugins. It is similar to the :fixture:`tmp_path`
    fixture but provides methods which aid in testing pytest itself.
    
src/_pytest/pytester.py