如何使用 pytest-mock 检查是否在单元测试中调用了函数？

Question

我有一个单元测试，我想检查一个函数是否被调用。我如何使用pytest 和pytest-mock 库来做到这一点？

例如，这是一个单元测试test_hello.py。在这个测试中，我调用函数 my_function 并想验证它是否使用给定的参数调用了 hello。

def hello(name):
    return f'Hello {name}'

def my_function():
    hello('Sam')

def test_hello(mocker):
    mocker.patch('hello')
    my_function()
    hello.assert_called_once_with('Sam')

上面的代码返回如下错误：

target = 'hello'

    def _get_target(target):
        try:
>           target, attribute = target.rsplit('.', 1)
E           ValueError: not enough values to unpack (expected 2, got 1)

/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/mock.py:1393: ValueError

During handling of the above exception, another exception occurred:

mocker = <pytest_mock.MockFixture object at 0x109c5e978>

    def test_hello(mocker):
>       mocker.patch('hello')

test_hello.py:8: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/pytest_mock.py:156: in __call__
    return self._start_patch(self.mock_module.patch, *args, **kwargs)
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/pytest_mock.py:134: in _start_patch
    p = mock_func(*args, **kwargs)
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/mock.py:1544: in patch
    getter, attribute = _get_target(target)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

target = 'hello'

    def _get_target(target):
        try:
            target, attribute = target.rsplit('.', 1)
        except (TypeError, ValueError):
            raise TypeError("Need a valid target to patch. You supplied: %r" %
>                           (target,))
E           TypeError: Need a valid target to patch. You supplied: 'hello'

/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/mock.py:1396: TypeError

Answer 1

解决错误

将mocked_hello 分配给mocked.patch

将side_effect 分配给模拟函数

def bonjour(name):
    return 'bonjour {}'.format(name)


def hello(name):
    return 'Hello {}'.format(name)


def my_function():
   return hello('Sam')


def test_hellow_differnt_from_module(mocker):
    # mocked func with `test_hello.py` as module name
    mocked_hello = mocker.patch('test_hello.hello')
    # assign side_effect to mocked func
    mocked_hello.side_effect = bonjour
    # the mocked func return_value changed by side_effect
    assert mocked_hello('Sam') == 'bonjour Sam'
    # the mocked func called with Sam, but with different return value
    mocked_hello.assert_called_with('Sam')

调用一个真正的函数 my_function() 并验证它是否调用了 hello

def test_my_function(mocker):
    mocker.patch('test_hello.hello', side_effect=bonjour)
    mf = my_function()
    hello.assert_called_with('Sam')
    assert mf == 'bonjour Sam'

Answer 2

我认为对 OP 的代码进行最小的更改以使其正常工作只是完全限定模拟函数的名称。因此，例如，如果代码位于名为 test.py 的文件中：

import pytest

def hello(name):
    return f'Hello {name}'

def my_function():
    hello('Sam')

def test_hello(mocker):
    mocker.patch('test.hello')
    my_function()
    hello.assert_called_once_with('Sam')

（我假设test.py 位于sys.path 的某个地方。）

但是，我认为最好将测试功能更改为：

def test_hello(mocker):
    mocked_func = mocker.patch('test.hello')
    my_function()
    mocked_func.assert_called_once_with('Sam')

这种形式对我来说似乎更清晰，并且不太可能在更复杂的代码中引发 AttributeError。