python - 测试期间出现断言错误，没有明确的错误消息

Question

这可能非常简单。

我写了这门课

class Pants :
    def __init__(self, pants_color, waist_size, length, price):
        self.color = pants_color
        self.waist_size = waist_size
        self.length = length
        self.price = price

    def change_price(self, new_price):
        self.price = new_price

    def discount(self, discount):
        self.price = self.price * (1 - discount)

我正在对其运行这些测试:

def check_results():
    pants = Pants('red', 35, 36, 15.12)
    assert pants.color == 'red'
    assert pants.waist_size == 35
    assert pants.length == 36
    assert pants.price == 15.12

    pants.change_price(10) == 10
    assert pants.price == 10 

    assert pants.discount(.1) == 9

    print('You made it to the end of the check. Nice job!')

check_results()

由于某种原因，我不断看到错误消息，但没有实际错误，它只是说 AssertionError:

    ---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-5-50abebbadc01> in <module>()
     13     print('You made it to the end of the check. Nice job!')
     14 
---> 15 check_results()

<ipython-input-5-50abebbadc01> in check_results()
      9     assert pants.price == 10
     10 
---> 11     assert pants.discount(.1) == 9
     12 
     13     print('You made it to the end of the check. Nice job!')

AssertionError: 

Answer 1

assert 只会打印您给出的错误消息，例如:

assert pants.discount(.1) == 9, "Pants discount should be {}, was {}".format(9, pants.discount(0.1))

会报错

AssertionError: Pants discount should be 9, was None

建议为每个断言语句添加一条消息。或者，您可以使用从 unittest 模块继承 UnitTest 的方法，并使用特殊的 assertEquals 方法，该方法具有内置的漂亮的错误打印功能。