Python 模拟失败调用断言

Question

我一直在阅读 python 模拟，但无法理解为什么以下代码失败。

我有两个类，一个 Potato 和一个 PotatoBag ，如下所示。 Figure 存储在 food.py 中，Report 存储在 bag.py 中。

class Potato:
    def create_potato(self):
        pass

    def output_potato(self):
        pass


class PotatoBag:
    def __init__(self, potatoes):
        self.potatoes = potatoes

    def output_to_file(self):
        for fig in self.potatoes:
            fig.create_potato()
            fig.output_potato()

目前，我正在尝试对输出方法进行单元测试，以便 Report 使用模拟正确地从 Figure 调用 create_figure 和 output_figure 。这是我的测试代码:

from unittest.mock import MagicMock, patch
from bag import PotatoBag
from food import Potato
import pytest

@pytest.fixture(scope='module')
def potatoes():
    x = Potato()
    y = Potato()
    return [x, y]

@patch('food.Potato')
def test_output_to_file(mock_potato, potatoes):

    test_potato_bag = PotatoBag(potatoes)
    test_potato_bag.output_to_file()

    mock_potato.return_value.create_potato.assert_called()
    mock_potato.return_value.output_potato.assert_called()

pytest 立即产生一个 AssertionError ，表明 create_figure 从未被调用。

_mock_self = <MagicMock name='Potato().create_potato' id='140480853451272'>

    def assert_called(_mock_self):
        """assert that the mock was called at least once
            """
        self = _mock_self
        if self.call_count == 0:
            msg = ("Expected '%s' to have been called." %
                   self._mock_name or 'mock')
>           raise AssertionError(msg)
E           AssertionError: Expected 'create_potato' to have been called.

/home/anaconda3/lib/python3.7/unittest/mock.py:792: AssertionError

我的代码有什么问题吗？

Answer 1

您正在向报告传递来自您的装置的图形列表，而不是模拟。

将您的测试更改为...

@patch('figure.Figure')
def test_output_to_file(mock_figure, figures):

    test_report = Report([mock_figure])
    test_report.output_to_file()

    mock_figure.create_figure.assert_called_once()
    mock_figure.output_figure.assert_called_once()

这解决了测试 output_to_file 正确调用 Figure 上的函数的问题，而无需实际担心设置图形并处理可能带来的任何副作用或额外复杂性调用这些函数。可以在 Figure 的单元测试中省去这种担忧;)