如何模拟具有未绑定方法的类？例如，这个类有一个@classmethod and a @staticmethod:
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。以下是一个工作示例，演示了我尝试过的事情。
Class Machine包含一个实例Calculator。我将进行测试Machine带着嘲笑Calculator。为了证明我的问题，Machine通过实例调用未绑定的方法Calculator并通过Calculator class:
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
上面的所有功能代码都可以正常工作。接下来是不起作用的部分。
我创建了一个模拟Calculator用于测试Machine:
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，绑定方法使用MockCalculator正如我所希望的那样。然而，呼吁Calculator.increment() and Calculator.decrement()仍在使用Calculator:
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
所以我尝试修补Calculator.increment() and Calculator.decrement():
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，未绑定的方法也需要一个实例Calculator作为一个论点：
类型错误：必须使用 Calculator 实例作为第一个参数调用未绑定的方法increment_proxy()（改为使用 int 实例）
如何模拟类方法Calculator.increment()和静态方法Calculator.decrement()?
