def _standard_os_environ():
    """Set up ``os.environ`` at the start of the test session to have
    standard values. Returns a list of operations that is used by
    :func:`._reset_os_environ` after each test.
    """
    mp = monkeypatch.MonkeyPatch()
    out = (
        (os.environ, "FLASK_ENV_FILE", monkeypatch.notset),
        (os.environ, "FLASK_APP", monkeypatch.notset),
        (os.environ, "FLASK_DEBUG", monkeypatch.notset),
        (os.environ, "FLASK_RUN_FROM_CLI", monkeypatch.notset),
        (os.environ, "WERKZEUG_RUN_MAIN", monkeypatch.notset),
    )

    for _, key, value in out:
        if value is monkeypatch.notset:
            mp.delenv(key, False)
        else:
            mp.setenv(key, value)

    yield out
    mp.undo()
Set up ``os.environ`` at the start of the test session to have
    standard values. Returns a list of operations that is used by
    :func:`._reset_os_environ` after each test.
    
tests/conftest.py