python - unittest.mock.patch 一个类实例，并设置方法返回值

Question

我有一个使用 Sensor 对象的 Alarm 对象。在我的测试中，我想用 Stub 修补 Sensor。下面的代码有效，但我必须将存根显式传递给 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)

我想做但似乎找不到实现的方法是用存根替换 Sensor 实例，而不将 anthing 传递给 Alarm 构造函数。这段代码在我看来应该可以工作，但不能：

    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 实例获取一个 MagicMock 实例，但“sample_pressure”方法不返回 22。基本上我想知道是否有一种方法可以使用 unittest.mock 来测试 Alarm 类，而无需使用 Sensor 实例的构造函数作为论据。

Answer 1

当您调用时，test_sensor_class.instance您正在使用test_sensor_class作为属性持有者，添加一个 Mock 属性instance，您添加一个 Mock 属性sample_pressure。您的补丁根本没有使用，您的代码实际上相当于：

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)

你想做什么修补调用Sensor().

使用您的代码，您只需将test_sensor_class模拟类的返回值设置为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)