Jest 无法测试等待的承诺，而是超时

Question

我从运行 axios GET 切换到返回 promise，现在我的 Jest 测试失败了：

正在下载 'resource.js' 中的 zip：

async function downloadMtgJsonZip() {
  const path = Path.resolve(__dirname, 'resources', fileName);
  const writer = Fs.createWriteStream(path);

  console.info('...connecting...');
  const { data, headers } = await axios({
    url,
    method: 'GET',
    responseType: 'stream',
  });
  return new Promise((resolve, reject) => {
    let error = null;
    const totalLength = headers['content-length'];
    const progressBar = getProgressBar(totalLength);
    console.info('...starting download...');
    data.on('data', (chunk) => progressBar.tick(chunk.length));
    data.pipe(writer);
    writer.on('error', (err) => {
      error = err;
      writer.close();
      reject(err);
    });
    writer.on('close', () => {
      const now = new Date();
      console.info(`Completed in ${(now.getTime() - progressBar.start) / 1000} seconds`);
      if (!error) resolve(true);
      // no need to call the reject here, as it will have been called in the
      // 'error' stream;
    });
  });
}

'resource.spec.js' 中的以下测试均未通过：

it('fetches successfully data from an URL', async () => {
    const onFn = jest.fn();
    const data = { status: 200, data: { pipe: () => 'data', on: onFn }, headers: { 'content-length': 100 } };

    const writerOnFn = jest.fn();

    axios.mockImplementationOnce(() => data);
    fs.createWriteStream.mockImplementationOnce(() => ({ on: writerOnFn }));
    await downloadMtgJsonZip();
    expect(onFn).toHaveBeenCalledWith('data', expect.any(Function));
    expect(axios).toHaveBeenCalledWith(
      expect.objectContaining({ url: 'https://mtgjson.com/api/v5/AllPrintings.json.zip' }),
    );
    expect(axios).toHaveBeenCalledWith(
      expect.objectContaining({ responseType: 'stream' }),
    );
  });
  it('ticks up the progress bar', async () => {
    const tickFn = jest.fn();
    const dataOnFn = jest.fn((name, func) => func(['chunk']));
    const data = { status: 200, data: { pipe: () => 'data', on: dataOnFn }, headers: { 'content-length': 1 } };

    const writerOnFn = jest.fn();

    ProgressBar.mockImplementationOnce(() => ({ tick: tickFn }));
    axios.mockImplementationOnce(() => data);
    fs.createWriteStream.mockImplementationOnce(() => ({ on: writerOnFn }));
    await downloadMtgJsonZip();

    expect(ProgressBar).toHaveBeenCalledWith(
      expect.stringContaining('downloading'),
      expect.objectContaining({
        total: 1,
      }),
    );
    expect(tickFn).toHaveBeenCalledWith(1);
  });
});

值得注意的是，VSCode 告诉我 'resource.js' 'this expression is not callable' 中的 axios 和 nothing mockImplementationOnce (它 'does not exist on type...').

以前我的 downloadMtgJsonZip 是这样的：

async function downloadMtgJsonZip() {
  const path = Path.resolve(__dirname, 'resources', 'AllPrintings.json.zip');
  const writer = Fs.createWriteStream(path);

  console.info('...connecting...');
  const { data, headers } = await axios({
    url,
    method: 'GET',
    responseType: 'stream',
  });
  const totalLength = headers['content-length'];
  const progressBar = getProgressBar(totalLength);
  const timer = setInterval(() => {
    if (progressBar.complete) {
      const now = new Date();
      console.info(`Completed in ${(now.getTime() - progressBar.start) / 1000} seconds`);
      clearInterval(timer);
    }
  }, 100);
  console.info('...starting download...');
  data.on('data', (chunk) => progressBar.tick(chunk.length));
  data.pipe(writer);
}

测试中唯一不同的是 createWriteStream 的模拟更简单（它显示为 fs.createWriteStream.mockImplementationOnce(() => 'fs');）

我试过添加：

  afterEach(() => { 
    jest.clearAllMocks(); 
    jest.resetAllMocks();
  });

我尝试添加 writerOnFn('close'); 来触发 writer.on('close', ...)。

但我一直收到这个错误：

: Timeout - Async callback was not invoked within the 5000 ms timeout specified by jest.setTimeout.Timeout - Async callback was not invoked within the 5000 ms timeout specified by jest.setTimeout.Error:

我无法弄清楚缺少什么，使异步调用成为 'invoked'。模拟 createWriteStream 解决了我的问题，但我没有看到任何其他模拟？

如何让这些测试再次通过？

Answer 1

Jest 完成异步测试的默认超时为 5000 毫秒（参考：https://jestjs.io/docs/configuration#testtimeout-number）

如果您有长时间的运行异步调用，则有必要提高此阈值。

例如在我的 jest.config.js 中超时设置为 60000ms

module.exports = {
  ...
  testTimeout: 60000, 
}

Answer 2

如何在测试代码中调用使用 writer.on(event, handler) 附加的事件处理程序？ writerOnFn 模拟不需要调用传入的处理函数吗？如果那些没有被调用，那么 resolve(true) 永远不会被调用，因此测试中对 await downloadMtgJsonZip(); 的调用永远不会解析。

我认为你需要这样的东西

const writerOnFn = jest.fn((e, cb) => if (e === 'close') cb())

当然，您可能想要充实它以区分 'error' 和 'close' 事件，或者如果您对 'error' 进行了测试，请务必更改它条件。

Jest 无法测试等待的承诺，而是超时

Jest can't test an awaited promise, it times out instead

javascript

testing

node.js

jestjs

axios