如何在 Python 上设置模拟异常行为？

Question

我正在使用定义内部异常 (github3.exceptions.UnprocessableEntity) 的外部库 (github3.py)。这个异常是如何定义的并不重要，所以我想创建一个副作用并设置我从这个异常中使用的属性。

经过测试的代码不是最小的示例：

import github3

class GithubService:
    def __init__(self, token: str) -> None:
        self.connection = github3.login(token=token)
        self.repos = self.connection.repositories()

    def create_pull(self, repo_name: str) -> str:
        for repo in self.repos:
            if repo.full_name == repo_name:
                break
        try:
            created_pr = repo.create_pull(
                title="title",
                body="body",
                head="head",
                base="base",
            )
        except github3.exceptions.UnprocessableEntity as github_exception:
            extra = ""
            for error in github_exception.errors:
                if "message" in error:
                    extra += f"{error['message']} "
                else:
                    extra += f"Invalid field {error['field']}. " # testing this case
            return f"{repo_name}: {github_exception.msg}. {extra}"

我需要从异常中设置属性 msg 和 errors。所以我在我的测试代码中尝试使用 pytest-mock:

@pytest.fixture
def mock_github3_login(mocker: MockerFixture) -> MockerFixture:
    """Fixture for mocking github3.login."""
    mock = mocker.patch("github3.login", autospec=True)
    mock.return_value.repositories.return_value = [
        mocker.Mock(full_name="staticdev/nope"),
        mocker.Mock(full_name="staticdev/omg"),
    ]
    return mock


def test_create_pull_invalid_field(
    mocker: MockerFixture, mock_github3_login: MockerFixture,
) -> None:
    exception_mock = mocker.Mock(errors=[{"field": "head"}], msg="Validation Failed")
    mock_github3_login.return_value.repositories.return_value[1].create_pull.side_effect = github3.exceptions.UnprocessableEntity(mocker.Mock())
    mock_github3_login.return_value.repositories.return_value[1].create_pull.return_value = exception_mock
    response = GithubService("faketoken").create_pull("staticdev/omg")

    assert response == "staticdev/omg: Validation Failed. Invalid field head."

此代码的问题在于，如果您有 side_effect 和 return_value，。

这里的问题是我不想知道 UnprocessableEntity 的实现来调用它，将正确的参数传递给它的构造函数。另外，我没有找到仅使用 side_effect 的其他方法。我还尝试使用 return 值并设置模拟的 class 并以这种方式使用它：

def test_create_pull_invalid_field(
    mock_github3_login: MockerFixture,
) -> None:
    exception_mock = Mock(__class__ = github3.exceptions.UnprocessableEntity, errors=[{"field": "head"}], msg="Validation Failed")
    mock_github3_login.return_value.repositories.return_value[1].create_pull.return_value = exception_mock
    response = GithubService("faketoken").create_pull("staticdev/omg")

    assert response == "staticdev/omg: Validation Failed. Invalid field head."

这个也不行，不抛异常。所以我不知道如何解决这个问题，因为我不想看到 UnprocessableEntity 的实现。这里有什么想法吗？

Answer 1

所以根据你的例子，你真的不需要模拟 github3.exceptions.UnprocessableEntity but only the incoming resp 参数。

所以下面的测试应该有效：

def test_create_pull_invalid_field(
    mocker: MockerFixture, mock_github3_login: MockerFixture,
) -> None:
    mocked_response = mocker.Mock()
    mocked_response.json.return_value = {
        "message": "Validation Failed", "errors": [{"field": "head"}]
    }

    repo = mock_github3_login.return_value.repositories.return_value[1]
    repo.create_pull.side_effect = github3.exceptions.UnprocessableEntity(mocked_response)
    response = GithubService("faketoken").create_pull("staticdev/omg")

    assert response == "staticdev/omg: Validation Failed. Invalid field head."

编辑：

如果你想要github3.exceptions.UnprocessableEntity to be completely abstracted, it won't be possible to mock the entire class as catching classes that do not inherit from BaseException is not allowed (See docs)。但是您可以仅通过模拟构造函数来解决它：

def test_create_pull_invalid_field(
    mocker: MockerFixture, mock_github3_login: MockerFixture,
) -> None:
    def _initiate_mocked_exception(self) -> None:
        self.errors = [{"field": "head"}]
        self.msg = "Validation Failed"

    mocker.patch.object(
        github3.exceptions.UnprocessableEntity, "__init__", 
        _initiate_mocked_exception
    )

    repo = mock_github3_login.return_value.repositories.return_value[1]
    repo.create_pull.side_effect = github3.exceptions.UnprocessableEntity
    response = GithubService("faketoken").create_pull("staticdev/omg")

    assert response == "staticdev/omg: Validation Failed. Invalid field head."

如何在 Python 上设置模拟异常行为？

How to set mocked exception behavior on Python?

unit-testing

exception

pytest

python-3.x

pytest-mock