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,我想用一个Stub修补Sensor.下面的代码可以工作,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,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实例获取一个MagicMock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来测试Alarm类而不需要一个带有Sensor实例的构造函数作为论点.

Answer 1

当您调用test_sensor_class.instance您test_sensor_class作为属性持有者时,添加Mock属性instance,您添加Mock属性sample_pressure.你的补丁根本就没用过,你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)

你想做什么打补丁的电话Sensor().

使用您的代码,您只需要将test_sensor_class模拟类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)