def test_frame_window_frame_notimplemented(self):
frame = WindowFrame()
msg = 'Subclasses must implement window_frame_start_end().'
with self.assertRaisesMessage(NotImplementedError, msg):
frame.window_frame_start_end(None, None, None)
def test_frame_empty_group_by_cols(self):
frame = WindowFrame()
self.assertEqual(frame.get_group_by_cols(), [])