Jest 异步函数总是 returns 未定义，从不解析

Question

我正在使用 axios 从 API 中获取一些用户数据并将它们推送到 vanilla JS 文件中的数组中，如下所示：

export async function fetchUsernames() {
  let usernames = [];
  axios.get("https://jsonplaceholder.typicode.com/users").then((users) => {
    for (let user of users.data) {
      usernames.push(user["username"]);
    }
    return usernames;
  });
}

问题是，即使当我将它与 React 连接时它在我的前端上正常工作，我的 jest 测试块总是得到 undefined 作为 return 值，即使虽然我使用 async/await。这是我的测试块：

test('Usernames get fetched properly', async () => {
  const usernames = await fetchUsernames();
  expect(usernames).toBe(expect.arrayContaining(['Brett']));
});

这是我收到的错误消息：

 × Usernames get fetched properly (17 ms)

  ● Usernames get fetched properly

    expect(received).toBe(expected) // Object.is equality

    Expected: ArrayContaining ["Brett"]
    Received: undefined

      12 | test('Usernames get fetched properly', async () => {
      13 |   const usernames = await fetchUsernames();
    > 14 |   expect(usernames).toBe(expect.arrayContaining(['Brett']));
         |                     ^
      15 | });

      at Object.<anonymous> (src/App.test.js:14:21)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 passed, 2 total
Snapshots:   0 total
Time:        4.038 s
Ran all test suites related to changed files.

这个问题背后最有可能的原因是什么？

Answer 1

更改 fetchUser 函数如下。

async function fetchUsernames() {
  let usernames = [];
  let users = await axios.get("https://jsonplaceholder.typicode.com/users");
  for (let user of users.data) {
    usernames.push(user["username"]);
  }
  return usernames;
}

这将 return 用户名数组。

test('Usernames get fetched properly', async () => {
  const usernames = await fetchUsernames();
  expect(usernames).toBe(expect.arrayContaining(['Brett']));
});

Jest 异步函数总是 returns 未定义，从不解析

Jest async function always returns undefined, never resolves

javascript

asynchronous

async-await

jestjs

axios