无法捕获模拟异常，因为它没有继承BaseException

Question

我正在做的一个项目涉及到连接到远程服务器，等待响应，然后根据响应执行操作。我们捕获了几个不同的异常，并且根据捕获的异常的不同而有不同的行为。例如：

def myMethod(address, timeout=20):
    try:
        response = requests.head(address, timeout=timeout)
    except requests.exceptions.Timeout:
        # do something special
    except requests.exceptions.ConnectionError:
        # do something special
    except requests.exceptions.HTTPError:
        # do something special
    else:
        if response.status_code != requests.codes.ok:
            # do something special
        return successfulConnection.SUCCESS

为了测试这一点，我们编写了一个如下所示的测试

class TestMyMethod(unittest.TestCase):

    def test_good_connection(self):
        config = {
            'head.return_value': type('MockResponse', (), {'status_code': requests.codes.ok}),
            'codes.ok': requests.codes.ok
        }
        with mock.patch('path.to.my.package.requests', **config):
            self.assertEqual(
                mypackage.myMethod('some_address',
                mypackage.successfulConnection.SUCCESS
            )

    def test_bad_connection(self):
        config = {
            'head.side_effect': requests.exceptions.ConnectionError,
            'requests.exceptions.ConnectionError': requests.exceptions.ConnectionError
        }
        with mock.patch('path.to.my.package.requests', **config):
            self.assertEqual(
                mypackage.myMethod('some_address',
                mypackage.successfulConnection.FAILURE
            )

ERROR: test_bad_connection (test.test_file.TestMyMethod)
----------------------------------------------------------------
Traceback (most recent call last):
  File "path/to/sourcefile", line ###, in myMethod
    respone = requests.head(address, timeout=timeout)
  File "path/to/unittest/mock", line 846, in __call__
    return _mock_self.mock_call(*args, **kwargs)
  File "path/to/unittest/mock", line 901, in _mock_call
    raise effect
my.package.requests.exceptions.ConnectionError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "Path/to/my/test", line ##, in test_bad_connection
    mypackage.myMethod('some_address',
  File "Path/to/package", line ##, in myMethod
    except requests.exceptions.ConnectionError:
TypeError: catching classes that do not inherit from BaseException is not allowed

Answer 1

我可以用一个最小的例子重现这个错误：

py：

class MyError(Exception):
    pass

class A:
    def inner(self):
        err = MyError("FOO")
        print(type(err))
        raise err
    def outer(self):
        try:
            self.inner()
        except MyError as err:
            print ("catched ", err)
        return "OK"

没有嘲讽的测试：

class FooTest(unittest.TestCase):
    def test_inner(self):
        a = foo.A()
        self.assertRaises(foo.MyError, a.inner)
    def test_outer(self):
        a = foo.A()
        self.assertEquals("OK", a.outer())

class FooTest(unittest.TestCase):
    def test_inner(self):
        a = foo.A()
        self.assertRaises(foo.MyError, a.inner)
    def test_outer(self):
        with unittest.mock.patch('foo.MyError'):
            a = exc2.A()
            self.assertEquals("OK", a.outer())

ERROR: test_outer (__main__.FooTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "...\foo.py", line 11, in outer
    self.inner()
  File "...\foo.py", line 8, in inner
    raise err
TypeError: exceptions must derive from BaseException

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<pyshell#78>", line 8, in test_outer
  File "...\foo.py", line 12, in outer
    except MyError as err:
TypeError: catching classes that do not inherit from BaseException is not allowed

这里我得到了第一个TypeError，这是您没有的，因为当您使用'requests.exceptions.connectionError':requests.exceptions.connectionError强制执行true异常时，我引发了一个mock。但是问题仍然是except子句试图捕获模拟。

TL/DR：当您模拟完整的requests包时，except requests.exceptions.ConnectionError子句试图捕获模拟。由于模拟不是真正的baseException，它会导致错误。

我所能想象的唯一解决方案是不模拟完整的请求，而只模拟不是异常的部分。我必须承认，除了这个以外，我找不到如何说mock mock所有东西，但是在您的示例中，您只需要修补requests.head。所以我认为这应该奏效：

def test_bad_connection(self):
    with mock.patch('path.to.my.package.requests.head',
                    side_effect=requests.exceptions.ConnectionError):
        self.assertEqual(
            mypackage.myMethod('some_address',
            mypackage.successfulConnection.FAILURE
        )

也就是说：只修补head方法，并将异常作为副作用。