def METHOD_NAME(self):
    ts1 = toggle_set(['one', 'two', 'three', '~one'])
    assert_equal(ts1, toggle_set(['~one', 'two', 'three']))
    ts1 = toggle_set(['~one', 'two', 'three', 'one'])
    assert_equal(ts1, toggle_set(['one', 'two', 'three']))