node.js - Jest : tests can't fail within setImmediate or process. nextTick 回调

Question

我正在尝试为需要在其 componentWillMount 方法中完成异步操作的 React 组件编写测试。 componentWillMount 调用一个函数，作为 prop 传递，它返回一个 promise ，我在测试中模拟了这个函数。

这工作正常，但如果测试在调用 setImmediate 或 process.nextTick 时失败，则 Jest 不会处理异常，它会提前退出。在下面，您可以看到我什至 try catch 此异常，但无济于事。

如何在 Jest 中使用 setImmediate 或 nextTick 之类的东西？这个问题的公认答案是我试图实现但未成功的:React Enzyme - Test `componentDidMount` Async Call .

it('should render with container class after getting payload', (done) => {
  let resolveGetPayload;
  let getPayload = function() {
    return new Promise(function (resolve, reject) {
      resolveGetPayload = resolve;
    });
  }
  const enzymeWrapper = mount(<MyComponent getPayload={getPayload} />);

  resolveGetPayload({
    fullname: 'Alex Paterson'
  });

  try {
    // setImmediate(() => {
    process.nextTick(() => {
      expect(enzymeWrapper.hasClass('container')).not.toBe(true); // Should and does fail
      done();
    });
  } catch (e) {
    console.log(e); // Never makes it here
    done(e);
  }
});

Jest v18.1.0

Node v6.9.1

Answer 1

另一个可能更清洁的解决方案，使用 async/await 并利用 jest/mocha 的能力来检测返回的 promise :

// async test utility function
function currentEventLoopEnd() {
  return new Promise(resolve => setImmediate(resolve));
}

it('should render with container class after getting payload', async () => {
  
  // mock the API call in a controllable way,
  // starts out unresolved
  let resolveGetPayload; // <- call this to resolve the API call
  let getPayload = function() {
    return new Promise(function (resolve, reject) {
      resolveGetPayload = resolve;
    });
  }
  
  // instanciate the component under state with the mock
  const enzymeWrapper = mount(<MyComponent getPayload={getPayload} />);
  expect(enzymeWrapper.hasClass('container')).not.toBe(true);

  resolveGetPayload({
    fullname: 'Alex Paterson'
  });

  await currentEventLoopEnd(); // <-- clean and clear !

  expect(enzymeWrapper.hasClass('container')).toBe(true);
});