由于 pytest 中的 Mocking 导致的 INTERNALERROR 覆盖率

Question

我正在尝试测试以下功能：

def my_testable_function(input_filename):
        if os.path.isfile(input_filename):
            return "Exist!"
        return "Not exist"

这是我第一次测试上面的功能：

def test_1():
    os.path.isfile = Mock(return_value=True)
    result = my_testable_function("/existing/path/file.txt")
    assert result == "Exist!"

运行 pytest==6.2.1 + pytest-cov==2.11.1:

$ py.test -v --ff --cov=<my_package> tests

我最终得到了 INTERNALERROR：

====================================================================== test session starts =======================================================================
platform darwin -- Python 3.8.5, pytest-6.2.1, py-1.10.0, pluggy-0.13.1 -- /Users/my-user/my-project/venv/bin/python3
cachedir: .pytest_cache
rootdir: /Users/my-user/my-project
plugins: cov-2.11.1, aiohttp-0.3.0
collected 6 items
run-last-failure: no previously failed tests, not deselecting items.

tests/test_app.py::test_1 PASSED                                                             [100%]
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/_pytest/main.py", line 269, in wrap_session
INTERNALERROR>     session.exitstatus = doit(config, session) or 0
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/_pytest/main.py", line 323, in _main
INTERNALERROR>     config.hook.pytest_runtestloop(session=session)
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/pluggy/hooks.py", line 286, in __call__
INTERNALERROR>     return self._hookexec(self, self.get_hookimpls(), kwargs)
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/pluggy/manager.py", line 93, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/pluggy/manager.py", line 84, in <lambda>
INTERNALERROR>     self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/pluggy/callers.py", line 203, in _multicall
INTERNALERROR>     gen.send(outcome)
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/pytest_cov/plugin.py", line 271, in pytest_runtestloop
INTERNALERROR>     self.cov_controller.finish()
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/pytest_cov/engine.py", line 44, in ensure_topdir_wrapper
INTERNALERROR>     return meth(self, *args, **kwargs)
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/pytest_cov/engine.py", line 230, in finish
INTERNALERROR>     self.cov.stop()
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/control.py", line 701, in combine
INTERNALERROR>     combine_parallel_data(
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/data.py", line 110, in combine_parallel_data
INTERNALERROR>     new_data.read()
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/sqldata.py", line 753, in read
INTERNALERROR>     with self._connect():       # TODO: doesn't look right
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/sqldata.py", line 298, in _connect
INTERNALERROR>     self._open_db()
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/sqldata.py", line 266, in _open_db
INTERNALERROR>     self._read_db()
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/sqldata.py", line 270, in _read_db
INTERNALERROR>     with self._dbs[get_thread_id()] as db:
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/sqldata.py", line 1037, in __enter__
INTERNALERROR>     self._connect()
INTERNALERROR>   File "/Users/my-user/my-project/venv/lib/python3.8/site-packages/coverage/sqldata.py", line 1019, in _connect
INTERNALERROR>     self.con = sqlite3.connect(filename, check_same_thread=False)
INTERNALERROR> sqlite3.OperationalError: unable to open database file

尝试用 monkeypatch 来做（没有 INTERNALERROR）：

def mock_is_file(filename):
    if filename == "/existing/path/file.txt":
        return True
    return os.path.isfile(filename)


def test_2(monkeypatch):
    monkeypatch.setattr(os.path, 'isfile', mock_is_file)
    my_testable_function("/existing/path/file.txt")
    assert result == "Exist!"

我的问题是，为什么在我第一次尝试时会发生这种情况，为什么在第二次尝试时会起作用？

Answer 1

当你放置模拟时，你还必须确保在测试结束时撤消模拟。您在测试中更改了 os.path.isfile，并保留更改。后来，coverage 需要那个函数，取而代之的是你的 mock。

monkeypatch 方法之所以有效，是因为 monkeypatch fixture 会在测试完成后自动清理 mock。

由于 pytest 中的 Mocking 导致的 INTERNALERROR 覆盖率

coverage INTERNALERROR due to Mocking in pytest

python

unit-testing

code-coverage

pytest

python-3.x