如何在 Python 中编写自定义的 `.assertFoo()` 方法? [英] How to write a custom `.assertFoo()` method in Python?

问题描述

我正在使用 Python 的 unittest 为我的应用程序编写一些测试用例.现在我需要将一个对象列表与另一个对象列表进行比较，以检查第一个列表中的对象是否符合我的预期.

I'm writing some test cases for my application using Python's unittest. Now I need to compare a list of objects with a list of another objects to check if the objects from the first list are what I'm expecting.

如何编写自定义 .assertFoo() 方法?它应该怎么做?它应该在失败时引发异常吗?如果是，哪个例外?以及如何传递错误信息?错误信息应该是 unicode 字符串还是字节字符串?

How can I write a custom .assertFoo() method? What should it do? Should it raise an exception on failure? If yes, which exception? And how to pass the error message? Should the error message be a unicode string or a bytestring?

遗憾的是，官方文档 没有解释如何编写自定义断言方法.

Unfortunately, the official documentation doesn't explain how to write custom assertion methods.

如果您需要一个真实的例子，请继续阅读.

If you need a real-world example for this, continue reading.

我写的代码有点像这样:

The code I'm writing is somewhat like this:

def assert_object_list(self, objs, expected):
    for index, (item, values) in enumerate(zip(objs, expected)):
        self.assertEqual(
            item.foo, values[0],
            'Item {0}: {1} != {2}'.format(index, item.foo, values[0])
        )
        self.assertEqual(
            item.bar, values[1],
            'Item {0}: {1} != {2}'.format(index, item.bar, values[1])
        )

def test_foobar(self):
    objs = [...]  # Some processing here
    expected = [
        # Expected values for ".foo" and ".bar" for each object
        (1, 'something'),
        (2, 'nothing'),
    ]
    self.assert_object_list(objs, expected)

这种方法可以非常轻松地以非常紧凑的方式描述每个对象的预期值，而无需实际创建完整的对象.

This approach makes it extremely easy to describe the expected values of each object in a very compact way, and without needing to actually create full objects.

然而……当一个对象断言失败时，不再比较其他对象，这使得调试更加困难.我想编写一个自定义方法，它可以无条件地比较所有对象，然后显示所有失败的对象，而不仅仅是第一个.

However... When one object fails the assertion, no further objects are compared, and this makes debugging a bit more difficult. I would like to write a custom method that would unconditionally compare all objects, and then would display all objects that failed, instead of just the first one.

推荐答案

我在这些情况下使用多重继承.例如:

I use the multiple inheritance in these cases. For example:

首先.我定义了一个包含将合并的方法的类.

First. I define a class with methods that will incorporate.

import os

class CustomAssertions:
    def assertFileExists(self, path):
        if not os.path.lexists(path):
            raise AssertionError('File not exists in path "' + path + '".')

现在我定义了一个继承自 unittest.TestCase 和 CustomAssertion 的类

Now I define a class that inherits from unittest.TestCase and CustomAssertion

import unittest

class MyTest(unittest.TestCase, CustomAssertions):
    def test_file_exists(self):
        self.assertFileExists('any/file/path')

if __name__ == '__main__':
    unittest.main()

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