def METHOD_NAME(self):
    payable = payables.get_payable(MockModel)
    MockPayable.immutable_model_fields_after_payment = ["test1", "test2"]
    self.assertEqual(
        ["test1", "test2"], payable.immutable_model_fields_after_payment
    )
    MockPayable.immutable_model_fields_after_payment = []
    self.assertEqual([], payable.immutable_model_fields_after_payment)
    self.assertEqual([], Payable.immutable_model_fields_after_payment)