'Test clear()'

def test_clears(self):

    test_son = SON([(1, 100), (2, 200), (3, 300)])
    test_son.clear()
    self.assertNotIn(1, test_son)
    self.assertEqual(0, len(test_son))
    self.assertEqual(0, len(test_son.keys()))
    self.assertEqual({}, test_son.to_dict())
