模拟全局变量 [英] Mocking a global variable

问题描述

我一直在尝试为模块实施一些单元测试.名为 alphabet.py 的示例模块如下:

I've been trying to implement some unit tests for a module. An example module named alphabet.py is as follows:

import database

def length_letters():
    return len(letters)

def contains_letter(letter):
    return True if letter in letters else False


letters = database.get('letters')   # returns a list of letters

我想用我选择的一些值模拟来自数据库的响应，但是下面的代码似乎不起作用.

I'd like to mock the response from a database with some values of my choice, but the code below doesn't seem to work.

import unittests  
import alphabet   
from unittest.mock import patch   


class TestAlphabet(unittest.TestCase): 
    @patch('alphabet.letters')
    def setUp(self, mock_letters):
        mock_letters.return_value = ['a', 'b', 'c']   

    def test_length_letters(self):
        self.assertEqual(3, alphabet.length_letters())

    def test_contains_letter(self):   
        self.assertTrue(alphabet.contains_letter('a'))

我已经看到很多例子，其中补丁"应用于方法和类，而不应用于变量.我不希望修补 database.get 方法，因为稍后我可能会再次将其与不同的参数一起使用，因此我将需要不同的响应.

I have seen many examples in which 'patch' is applied to methods and classes, but not to variables. I prefer not to patch the method database.get because I may use it again with different parameters later on, so I would need a different response.

我在做什么错了?

推荐答案

尝试一下:

import unittests  
import alphabet   
from unittest.mock import patch   


class TestAlphabet(unittest.TestCase): 
    def setUp(self):
        self.mock_letters = mock.patch.object(
            alphabet, 'letters', return_value=['a', 'b', 'c']
        )

    def test_length_letters(self):
        with self.mock_letters:
            self.assertEqual(3, alphabet.length_letters())

    def test_contains_letter(self):
        with self.mock_letters:
            self.assertTrue(alphabet.contains_letter('a'))

您需要在单个测试实际运行时应用模拟，而不仅仅是在setUp()中.我们可以在setUp()中创建该模拟，然后在以后的with ...上下文管理器中将其应用.

You need to apply the mock while the individual tests are actually running, not just in setUp(). We can create the mock in setUp(), and apply it later with a with ... Context Manager.

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