Question

我有一个使用Sensor对象的Alarm对象。在我的测试中，我想用一个Stub修补Sensor。下面的代码有效，但我必须明确地将存根传递给Alarm构造函数：

#tire_pressure_monitoring.py
from sensor import Sensor

class Alarm:

    def __init__(self, sensor=None):
        self._low_pressure_threshold = 17
        self._high_pressure_threshold = 21
        self._sensor = sensor or Sensor()
        self._is_alarm_on = False

    def check(self):
        psi_pressure_value = self._sensor.sample_pressure()
        if psi_pressure_value < self._low_pressure_threshold or self._high_pressure_threshold < psi_pressure_value:
            self._is_alarm_on = True

    @property
    def is_alarm_on(self):
        return self._is_alarm_on

#test_tire_pressure_monitoring.py
import unittest
from unittest.mock import patch, MagicMock, Mock

from tire_pressure_monitoring import Alarm
from sensor import Sensor

class AlarmTest(unittest.TestCase):

    def test_check_with_too_high_pressure(self):
        with patch('tire_pressure_monitoring.Sensor') as test_sensor_class:
            test_sensor_class.instance.sample_pressure.return_value=22
            alarm = Alarm(sensor=test_sensor_class.instance)
            alarm.check()
            self.assertTrue(alarm.is_alarm_on)

我想做的，但似乎无法找到实现的方法，就是用存根替换Sensor实例，而不将Anthing传递给Alarm构造函数。这段代码看起来像我应该工作，但不是：

    def test_check_with_too_high_pressure(self):
    with patch('tire_pressure_monitoring.Sensor') as test_sensor_class:
        test_sensor_class.instance.sample_pressure.return_value=22
        alarm = Alarm()
        alarm.check()
        self.assertTrue(alarm.is_alarm_on)

Alarm实例获取MagicMock的实例，但'sample_pressure'方法不返回22.基本上我想知道是否有办法使用unittest.mock测试Alarm类而不需要构造函数传感器实例作为参数。

Answer 1

当您致电test_sensor_class.instance时，您正在使用test_sensor_class作为财产所有者，请添加Mock属性instance，并向其添加模拟属性sample_pressure。您的补丁根本没有使用，您的代码实际上等同于：

def test_check_with_too_high_pressure(self):
    instance = MagicMock()
    instance.sample_pressure.return_value=22
    alarm = Alarm(sensor=instance)
    alarm.check()
    self.assertTrue(alarm.is_alarm_on)

你想做什么修补Sensor()的号召。

使用您的代码，您只需将模拟类test_sensor_class的返回值设置为预设模拟Sensor。

def test_check_with_too_high_pressure(self):
    with patch('tire_pressure_monitoring.Sensor') as test_sensor_class:
        mockSensor = MagicMock()
        mockSensor.sample_pressure.return_value = 22
        test_sensor_class.return_value = mockSensor
        alarm = Alarm()
        alarm.check()
        self.assertTrue(alarm.is_alarm_on)

unittest.mock.patch一个类实例，并设置方法返回值

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