AssertionError在测试过程中没有明确的错误消息

Question

这可能是很简单的事情。

我写过这门课

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)

我正在做这些测试：

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()

出于某种原因，我一直看到一个没有实际错误的错误消息，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只会打印您提供的错误消息，例如：

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

会给出错误

AssertionError: Pants discount should be 9, was None

建议为每个assert语句添加一条消息。或者，您可以使用从UnitTest继承的unittest模块，并使用专门的assertEquals方法，该方法内置了相当错误的打印。

Answer 2

是的，显然我不得不增加一个return，而不是仅仅设置新的价格。不过，我还是会分享的，以防另一个人包围它。

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