javascript - React Native 异步 Jest 组件测试

Question

我有一个组件在装载时分派(dispatch) fetch 请求，并显示结果。

我正尝试在请求完成后创建此组件的测试快照。很长一段时间以来，我一直在努力解决这个问题，这里是关于 SO 的相关问题，但我没有运气:

1. Async component snapshot using Jest and Redux
2. How do test async components with Jest?
3. React+Jest - Testing async components and waiting for mount
4. How to take a jest snapshot after axios fetched data in componentDidMount?

这是我的fetch 模拟:

// Mocking the global.fetch included in React Native
global.fetch = jest.fn()

// Helper to mock a success response (only once)
fetch.mockResponseSuccess = (body, status = 200) => {
    fetch.mockImplementationOnce(() =>
        Promise.resolve({
            status,
            json: () => Promise.resolve(JSON.parse(body))
        })
    )
}

// Helper to mock a failure response (only once)
fetch.mockResponseFailure = error => {
    fetch.mockImplementationOnce(() => Promise.reject(error))
}

组件(简化):

export class Posts extends Component {
    constructor(props) {
        super(props)
        this.state = {
            items: [],
            loading: false
        }
        this._getItems()
    }

    async _getItems() {
        const resp = await fetch(
                "/user/recent_posts",
                {
                    method: "GET"
                }
            )
        this.setState({
            items: resp.json["data"],
        })
    }

    render() {
        // renders this.state.items
    }

这是测试:

    test("view renders correctly", async done => {
        fetch.mockResponseSuccess(
            JSON.stringify({
                data: [
                    { caption: "test", likes: 100 },
                    { caption: "test2", likes: 200 }
                ]
            })
        )
        // also tried with setTimeout and setImidiate
        const wrapper = await shallow(<Posts />) // also tried with react-test-renderer
        await wrapper.update() // didn't work with or without
        // await waitForState(wrapper, state => state.loading === false) --> didn't work
        // process.nextTick(() => {.... --> didn't work
        // jest.runTimersToTime(1) --> didn't work
        expect(wrapper).toMatchSnapshot()
        done()
    })

问题是快照中的this.state.items总是空的。

Answer 1

为了将来引用，以下是为我解决的问题:

test("view renders correctly", done => {
    // mock response here...
    const wrapper = shallow(<Posts />)
    setImmediate(() => {
        wrapper.update()
        try {
            expect(wrapper).toMatchSnapshot()
        } catch (e) {
            console.log(e)
        }

        done()
    })
})