def test_calculates_balance_correctly(self):
        source = Source(
            amount_allocated=D('100'),
            amount_debited=D('80'),
            amount_refunded=D('20'))
        self.assertEqual(
            D('80') + D('20') - D('100'), source.balance)
dataset/ETHPy150Open django-oscar/django-oscar/tests/unit/payment/model_tests.py/TestSource.test_calculates_balance_correctly/swapped operands of `-`