关于单元测试：如何模拟Python静态方法和类方法


How to mock Python static methods and class methods

如何模拟具有未绑定方法的类？例如，这个类有一个@classmethod和一个@staticmethod：

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class Calculator(object):
    def __init__(self, multiplier):
        self._multiplier = multiplier
    def multiply(self, n):
        return self._multiplier * n
    @classmethod
    def increment(cls, n):
        return n + 1
    @staticmethod
    def decrement(n):
        return n - 1

calculator = Calculator(2)
assert calculator.multiply(3) == 6    
assert calculator.increment(3) == 4
assert calculator.decrement(3) == 2
assert Calculator.increment(3) == 4
assert Calculator.decrement(3) == 2

上面几乎描述了我的问题。下面是一个工作示例，演示了我尝试过的事情。

类Machine包含Calculator的实例。我将用一个Calculator的模型来测试Machine。为了证明我的问题，Machine通过Calculator的实例和Calculator类调用了未绑定的方法：

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class Machine(object):
    def __init__(self, calculator):
        self._calculator = calculator
    def mult(self, n):
        return self._calculator.multiply(n)
    def incr_bound(self, n):
        return self._calculator.increment(n)
    def decr_bound(self, n):
        return self._calculator.decrement(n)
    def incr_unbound(self, n):
        return Calculator.increment(n)
    def decr_unbound(self, n):
        return Calculator.decrement(n)

machine = Machine(Calculator(3))
assert machine.mult(3) == 9

assert machine.incr_bound(3) == 4
assert machine.incr_unbound(3) == 4

assert machine.decr_bound(3) == 2
assert machine.decr_unbound(3) == 2

上面所有的功能代码都可以正常工作。接下来是不起作用的部分。

我创建了一个用于测试Machine的Calculator的模拟模型：

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from mock import Mock

def MockCalculator(multiplier):
    mock = Mock(spec=Calculator, name='MockCalculator')

    def multiply_proxy(n):
        '''Multiply by 2*multiplier instead so we can see the difference'''
        return 2 * multiplier * n
    mock.multiply = multiply_proxy

    def increment_proxy(n):
        '''Increment by 2 instead of 1 so we can see the difference'''
        return n + 2
    mock.increment = increment_proxy

    def decrement_proxy(n):
        '''Decrement by 2 instead of 1 so we can see the difference'''
        return n - 2
    mock.decrement = decrement_proxy

    return mock

在下面的单元测试中，绑定方法如我所希望的那样使用MockCalculator。但是，对Calculator.increment()和Calculator.decrement()的调用仍然使用Calculator：

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import unittest

class TestMachine(unittest.TestCase):
    def test_bound(self):
        '''The bound methods of Calculator are replaced with MockCalculator'''
        machine = Machine(MockCalculator(3))
        self.assertEqual(machine.mult(3), 18)
        self.assertEqual(machine.incr_bound(3), 5)
        self.assertEqual(machine.decr_bound(3), 1)

    def test_unbound(self):
        '''Machine.incr_unbound() and Machine.decr_unbound() are still using
        Calculator.increment() and Calculator.decrement(n), which is wrong.
        '''
        machine = Machine(MockCalculator(3))
        self.assertEqual(machine.incr_unbound(3), 4)    # I wish this was 5
        self.assertEqual(machine.decr_unbound(3), 2)    # I wish this was 1

所以我试着给Calculator.increment()和Calculator.decrement()打补丁：

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def MockCalculatorImproved(multiplier):
    mock = Mock(spec=Calculator, name='MockCalculatorImproved')

    def multiply_proxy(n):
        '''Multiply by 2*multiplier instead of multiplier so we can see the difference'''
        return 2 * multiplier * n
    mock.multiply = multiply_proxy
    return mock

def increment_proxy(n):
    '''Increment by 2 instead of 1 so we can see the difference'''
    return n + 2

def decrement_proxy(n):
    '''Decrement by 2 instead of 1 so we can see the difference'''
    return n - 2


from mock import patch

@patch.object(Calculator, 'increment', increment_proxy)
@patch.object(Calculator, 'decrement', decrement_proxy)
class TestMachineImproved(unittest.TestCase):
    def test_bound(self):
        '''The bound methods of Calculator are replaced with MockCalculator'''
        machine = Machine(MockCalculatorImproved(3))
        self.assertEqual(machine.mult(3), 18)
        self.assertEqual(machine.incr_bound(3), 5)
        self.assertEqual(machine.decr_bound(3), 1)

    def test_unbound(self):
        '''machine.incr_unbound() and Machine.decr_unbound() should use
        increment_proxy() and decrement_proxy(n).
        '''
        machine = Machine(MockCalculatorImproved(3))
        self.assertEqual(machine.incr_unbound(3), 5)
        self.assertEqual(machine.decr_unbound(3), 1)

即使在修补之后，未绑定的方法也希望使用Calculator的实例作为参数：

TypeError: unbound method increment_proxy() must be called with Calculator instance as first argument (got int instance instead)

如何模拟类方法Calculator.increment()和静态方法Calculator.decrement()？

你在修补错误的对象。您必须从Machine类修补Calculator，而不是一般的Calculator类。在这里阅读。

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from mock import patch
import unittest

from calculator import Calculator
from machine import Machine


class TestMachine(unittest.TestCase):
    def my_mocked_mult(self, multiplier):
        return 2 * multiplier * 3
    def test_bound(self):
        '''The bound methods of Calculator are replaced with MockCalculator'''
        machine = Machine(Calculator(3))
        with patch.object(machine,"mult") as mocked_mult:
            mocked_mult.side_effect = self.my_mocked_mult
            self.assertEqual(machine.mult(3), 18)
            self.assertEqual(machine.incr_bound(3), 5)
            self.assertEqual(machine.decr_bound(3), 1)

    def test_unbound(self):
        '''Machine.incr_unbound() and Machine.decr_unbound() are still using
        Calculator.increment() and Calculator.decrement(n), which is wrong.
        '''
        machine = Machine(Calculator(3))
        self.assertEqual(machine.incr_unbound(3), 4)    # I wish this was 5
        self.assertEqual(machine.decr_unbound(3), 2)    # I wish this was 1
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C++、Java和C++程序员往往在Python中过度使用类和静态方法。Python疗法是使用模块功能。

因此，首先，这里是正在测试的重构软件，方法increment()和decrement()作为模块函数。界面确实发生了变化，但功能相同：

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# Module machines

class Calculator(object):
    def __init__(self, multiplier):
        self._multiplier = multiplier
    def multiply(self, n):
        return self._multiplier * n

def increment(n):
    return n + 1

def decrement(n):
    return n - 1

calculator = Calculator(2)
assert calculator.multiply(3) == 6
assert increment(3) == 4
assert decrement(3) == 2


class Machine(object):
    '''A larger machine that has a calculator.'''
    def __init__(self, calculator):
        self._calculator = calculator
    def mult(self, n):
        return self._calculator.multiply(n)
    def incr(self, n):
        return increment(n)
    def decr(self, n):
        return decrement(n)

machine = Machine(Calculator(3))
assert machine.mult(3) == 9
assert machine.incr(3) == 4
assert machine.decr(3) == 2

将函数increment_mock()和decrement_mock()添加到模拟increment()和decrement()中：

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from mock import Mock
import machines

def MockCalculator(multiplier):
    mock = Mock(spec=machines.Calculator, name='MockCalculator')

    def multiply_proxy(n):
        '''Multiply by 2*multiplier instead of multiplier so we can see the
        difference.
        '''
        return 2 * multiplier * n
    mock.multiply = multiply_proxy

    return mock

def increment_mock(n):
    '''Increment by 2 instead of 1 so we can see the difference.'''
    return n + 2

def decrement_mock(n):
    '''Decrement by 2 instead of 1 so we can see the difference.'''
    return n - 2

现在就好了。补丁increment()和decrement()，用它们的模型替换它们：

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import unittest
from mock import patch
import machines

@patch('machines.increment', increment_mock)
@patch('machines.decrement', decrement_mock)
class TestMachine(unittest.TestCase):
    def test_mult(self):
        '''The bound method of Calculator is replaced with MockCalculator'''
        machine = machines.Machine(MockCalculator(3))
        self.assertEqual(machine.mult(3), 18)

    def test_incr(self):
        '''increment() is replaced with increment_mock()'''
        machine = machines.Machine(MockCalculator(3))
        self.assertEqual(machine.incr(3), 5)

    def test_decr(self):
        '''decrement() is replaced with decrement_mock()'''
        machine = machines.Machine(MockCalculator(3))
        self.assertEqual(machine.decr(3), 1)
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