python-3.x - 协程的 Python 3.8 模拟

Question

我尝试编写单元测试来检查类方法是否被断言。

class Application:
    async def func1(self):
        await self.func2(self.func3())

    async def func2(self, val):
        pass

    async def func3(self):
        pass

并对其进行单元测试:

@pytest.mark.asyncio
async def test_method():
    app = Application()

    with patch.object(Application, 'func2') as mock:
        await app.func1()
        mock.assert_awaited_with(app.func3())

但我得到错误:

AssertionError: expected await not found.
Expected: func2(<coroutine object Application.func3 at 0x7f1ecf8557c0>)
Actual: func2(<coroutine object Application.func3 at 0x7f1ecf855540>)

为什么？我调用了相同的方法。我能用它做什么？

Answer 1

有一个asynctest这使得模拟(修补)异步函数变得更容易。

Patching

Patching is a mechanism allowing to temporarily replace a symbol (class, object, function, attribute, …) by a mock, in-place. It is especially useful when one need a mock, but can’t pass it as a parameter of the function to be tested.

For instance, if cache_users() didn’t accept the client argument, but instead created a new client, it would not be possible to replace it by a mock like in all the previous examples.

When an object is hard to mock, it sometimes shows a limitation in the design: a coupling that is too tight, the use of a global variable (or a singleton), etc. However, it’s not always possible or desirable to change the code to accomodate the tests. A common situation where tight coupling is almost invisible is when performing logging or monitoring. In this case, patching will help.

A patch() can be used as a context manager. It will replace the target (logging.debug()) with a mock during the lifetime of the with block.

async def test_with_context_manager(self):
    client = asynctest.Mock(AsyncClient())
    cache = {}

    with asynctest.patch("logging.debug") as debug_mock:
        await cache_users_async(client, cache)

    debug_mock.assert_called()

请注意，函数的路径以字符串形式提供给 asynctest.patch而不是作为一个对象。

另外，在 func1 func2在获取 func3作为协程，不等待它运行(无等待)。

你可以尝试这样的事情:

import asynctest
@pytest.mark.asyncio
async def test_method():
    app = Application()

    with asynctest.patch('Application.func2') as mock:
        await app.func1()
    mock.assert_awaited_with(app.func3())