javascript - 你如何为 getInitialProps 编写 Jest 测试？

Question

static async getInitialProps({ query }) {
  let content;
  let alert;

  try {
    const first = query.first ? query.first : '';
    content = await getContent(first);
  } catch (error) {
    alert = 'There was an error loading data, please try again.';
    content = [];
  }

  return {
    content,
    alert,
  };
}

我正在尝试为这个逻辑编写测试，但因为它是服务器端代码，所以我很难理解如何为它编写测试，因为它在 instance() 中不可用。

Google 没有向我展示这方面的方法，所以我想知道其他人是如何处理 getInitial Prop 的编写测试的。

Answer 1

首先，看一下什么是static method static keyword 是什么意思做。

由于 getInitialProps 只是组件上的一个静态函数，您可以像测试任何其他函数一样手动测试它。

import MyComponent from "./path/to/MyComponent";

// Mock the getContent function which I don't know where it comes from.
jest.mock("../someModule.js", () => ({
  getContent: () => Promise.reject()
}));

describe("MyComponent", () => {
  it('populates the "alert" prop on getContent failure.', async () => {
    // Inject anything you want to test
    const props = await MyComponent.getInitialProps({
      query: { first: "whatever" }
    });

    // And make sure it results in what you want.
    expect(props).toEqual({
      content: [],
      alert: "There was an error loading data, please try again."
    });
  });
});

大多数时候，getInitialProps is called like that anyway .

export default class MyApp extends App {
  static async getInitialProps ({ Component, router, ctx }) {
    let pageProps = {}

    if (Component.getInitialProps) {
      pageProps = await Component.getInitialProps(ctx)
    }

    return { pageProps }
  }

documentation describes getInitialProps goal并且我们可以确认可以直接调用它并测试它的返回值作为 Object。

Notice that to load data when the page loads, we use getInitialPropswhich is an async static method. It can asynchronously fetchanything that resolves to a JavaScript plain Object, which populatesprops.

Data returned from getInitialProps is serialized when serverrendering, similar to a JSON.stringify. Make sure the returnedobject from getInitialProps is a plain Object and not usingDate, Map or Set.

For the initial page load, getInitialProps will execute on theserver only. getInitialProps will only be executed on the clientwhen navigating to a different route via the Link component or usingthe routing APIs.