如何模拟类中对象的方法？答案

【问题标题】：How to mock a method on an object in a class?如何模拟类中对象的方法？
【发布时间】：2020-04-20 23:51:03
【问题描述】：

我正在尝试弄清楚如何使用额外的间接级别进行模拟 - 类中对象的方法。

import serial

class MyClass(object):

  def __init__(self, com_port, baudrate):
      self.sp = serial.Serial(com_port, baudrate)

  def do_something(self, data):
      num_bytes_written = self.sp.write(data)
      if num_bytes_written != len(data):
          return -1
      return 0

在测试文件中：

import mock

...

@mock.patch('serial.Serial', return_value='')
@mock.patch('serial.Serial.write', return_value=0)
def test_do_something_fails_on_bad_write(self, mock_write):
    ...
    want = -1
    dummy_data = b'123'
    inst = myfile.MyClass('COM8', 115200)
    got = c.do_something(dummy_data)
    self.assertEqual(got, want)

【问题讨论】：

标签： python-2.7 mocking python-unittest python-mock

【解决方案1】：

单元测试解决方案：

serial.py:

class Serial(object):
    def __init__(self, port, baudrate):
        self.port = port
        self.baudrate = baudrate

    def write(self, data):
        return 100

myclass.py:

import serial


class MyClass(object):

    def __init__(self, com_port, baudrate):
        self.sp = serial.Serial(com_port, baudrate)

    def do_something(self, data):
        num_bytes_written = self.sp.write(data)
        if num_bytes_written != len(data):
            return -1
        return 0

test_myclass.py:

import unittest
from unittest import mock
import serial
import myclass


class TestMyClass(unittest.TestCase):
    @mock.patch('myclass.serial.Serial')
    def test_do_something_fails_on_bad_write(self, mock_Serial):
        serial_instance = mock_Serial()
        serial_instance.write.return_value = 1
        want = -1
        dummy_data = b'123'
        c = myclass.MyClass('COM8', 115200)
        got = c.do_something(dummy_data)
        self.assertEqual(got, want)
        serial_instance.write.assert_called_once_with(b'123')

    @mock.patch('myclass.serial.Serial')
    def test_do_something_success(self, mock_Serial):
        serial_instance = mock_Serial()
        serial_instance.write.return_value = 3
        want = 0
        dummy_data = b'123'
        c = myclass.MyClass('COM8', 115200)
        got = c.do_something(dummy_data)
        self.assertEqual(got, want)
        serial_instance.write.assert_called_once_with(b'123')


if __name__ == '__main__':
    unittest.main()

带有覆盖率报告的单元测试结果：

..
----------------------------------------------------------------------
Ran 2 tests in 0.002s

OK
Name                                         Stmts   Miss  Cover   Missing
--------------------------------------------------------------------------
src/stackoverflow/61333922/myclass.py            9      0   100%
src/stackoverflow/61333922/serial.py             6      3    50%   3-4, 7
src/stackoverflow/61333922/test_myclass.py      25      0   100%
--------------------------------------------------------------------------
TOTAL                                           40      3    92%

【讨论】：