def test_flatten_empty(self): self.assertEqual([], list_ops.flat([]))
def test_flatten_once(self): self.assertEqual(["x", "y", "z"], list_ops.flat([["x", "y", "z"]]))
def test_flatten_nested(self): self.assertEqual([1, 2, 3, 4], list_ops.flat([[[1, 2], [3]], [[4]]]))