Question

在python中使用mockito进行单元测试时，我遇到了一个无法找到解决方案的问题。我试图在给定的类方法中修补io.BytesIO的用法。以下代码显示了出现问题的简化版本：

from mockito import mock, patch, when
from io import BytesIO

class Foo:
    def bar(self):
        buffer = io.BytesIO()
        # ...
        return buffer.getvalue()

def test_foo():
    bytesIO_mock = mock(strict=True)
    when(bytesIO_mock).getvalue().thenReturn('data')

    patch(BytesIO.__new__, lambda: bytesIO_mock)
    result = Foo().bar()
    assert result == 'data'

执行测试时出现以下错误：

/venv/lib/python3.6/site-packages/mockito/mockito.py:270: in patch
when2(fn, Ellipsis).thenAnswer(replacement)
/venv/lib/python3.6/site-packages/mockito/mockito.py:245: in when2
return invocation.StubbedInvocation(theMock, name)(*args, **kwargs)
/venv/lib/python3.6/site-packages/mockito/invocation.py:284: in __call__
self.mock.stub(self.method_name)
/venv/lib/python3.6/site-packages/mockito/mocking.py:117: in stub
self.replace_method(method_name, original_method)
/venv/lib/python3.6/site-packages/mockito/mocking.py:108: in replace_method
self.set_method(method_name, new_mocked_method)

self = <mockito.mocking.Mock object at 0x10d50cb38>, method_name = '__new__'
new_method = <function Mock.replace_method.<locals>.new_mocked_method at 0x10d753e18>

    def set_method(self, method_name, new_method):
>       setattr(self.mocked_obj, method_name, new_method)
E       TypeError: can't set attributes of built-in/extension type '_io.BytesIO'

/venv/lib/python3.6/site-packages/mockito/mocking.py:74: TypeError

是否有解决此问题的方法，或者只是在python中无法模拟某些对象？

Answer 1

您可以简单地模仿来自patch的响应，而不是使用io.BytesIO()，如下所示：

def test_foo():
    bytesIO_mock = mock(strict=True)

    when(bytesIO_mock).getvalue().thenReturn('data')
    when(io).BytesIO().thenReturn(bytesIO_mock)

    result = Foo().bar()
    assert result == 'data'

根据经验，Python中的所有对象都可以被模拟as everything in Python is an object。如果您无法模拟它，可能是由于正在使用的测试库/框架的限制。

如何使用mockito在python中修补内置/扩展类型？

1 个答案: