def test_correct_source_expressions(self):
func = StatAggregate(x='test', y=13)
self.assertIsInstance(func.source_expressions[0], Value)
self.assertIsInstance(func.source_expressions[1], F)
def test_missing_arguments_raises_exception(self):
with self.assertRaisesMessage(ValueError,
'Both y and x must be provided.'):
StatAggregate(x=None, y=None)