def test_mixedSingleItemsAreSumOfIndividualPrices(self):
    self.assertEqual(checkout('BADC'), (((checkout('A') + checkout('B')) + checkout('C')) + checkout('D')))
def test_mixedSingleItemsAreSumOfIndividualPrices(self):
    self.assertEqual(checkout('BADC'), (((checkout('A') + checkout('B')) + checkout('C')) + checkout('D')))