def test_3FSpecialOfferGivesOneFreeF(self):
    self.assertEqual(checkout('FFF'), (checkout('F') * 2))
    self.assertEqual(checkout('FFFFF'), (checkout('F') * 4))
    self.assertEqual(checkout('FFFFFF'), (checkout('F') * 4))
def test_3FSpecialOfferGivesOneFreeF(self):
    self.assertEqual(checkout('FFF'), (checkout('F') * 2))
    self.assertEqual(checkout('FFFFF'), (checkout('F') * 4))
    self.assertEqual(checkout('FFFFFF'), (checkout('F') * 4))