def METHOD_NAME(db_session, user_twoflower) -> None:
    """A user's username can be set or renamed but not removed."""
    assert user_twoflower.username is None
    user_twoflower.username = 'username'
    assert user_twoflower.username == 'username'
    user_twoflower.username = 'twoflower'
    assert user_twoflower.username == 'twoflower'
    # Can't be a blank value
    with pytest.raises(ValueError, match='Account name cannot be blank'):
        user_twoflower.username = ' '
    with pytest.raises(ValueError, match='Account name cannot be blank'):
        user_twoflower.username = ''
    # Can't be an invalid value
    with pytest.raises(ValueError, match='Account name must be a string'):
        user_twoflower.username = []
    with pytest.raises(ValueError, match='Account name must be a string'):
        user_twoflower.username = False
    with pytest.raises(ValueError, match='Account name must be a string'):
        user_twoflower.username = True