如何测试嵌入式异步调用 | 如何测试嵌入式异步调用

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问题描述

我正在测试函数 parent()，该函数调用返回的函数 slomo().我想检查 .then()中的代码是否正在执行.

I am testing a function parent() that calls a function slomo() that returns a promise. I want to check that the code within the .then() is being executed.

function slomo() {
  return new Promise(function (resolve, reject) {
    resolve('good')
    reject('bad')
  })
}

child = jest.fn()

function parent() {
  slomo()
    .then((result) => {
      child()
    })
}

// TEST

it('runs child', () => {
  parent()
  expect(child).toHaveBeenCalledTimes(1)
})

结果是:

我已确认通过 console.log 调用了子功能，但是在测试完成后 AFTER 已记录该子功能.
我尝试通过并在测试内调用 done ，但这不能解决问题.
也许上面的代码是反模式，需要重写才能进行测试?

I have confirmed the child function IS being called via console.log, but it is being logged AFTER the test has completed.
I have tried passing and calling done inside the test but that did not correct the issue.
Maybe the above code is an anti-pattern and needs to be rewritten so that it can be tested?

非常感谢您能给我的帮助！

Any help you can give me is greatly appreciated!

推荐答案

您正确地发现了问题的根本原因，即测试早于异步代码完成，因此测试应正确跟踪异步.但是似乎您丢失了承诺b/c，但您没有将其退还，所以:

You correctly found the root case of the problem, that test finishes earlier then async code, so test should track async correctly. But seems to you lost the promise b/c you don't return it, so:

function parent() {
  return slomo() // <<<--- add return
    .then((result) => {
      child()
    })
}

接下来，您只需添加完成:

it('runs child', (done) => { // <<<< --- add done
  parent().then(() => {
    expect(child).toHaveBeenCalledTimes(1)
    done(); // <<<< -- done should be called after all
  })
});

或只返回承诺:

it('runs child', () => {
  return parent().then(() => {  // <<<--- return
    expect(child).toHaveBeenCalledTimes(1);
  })
})

希望有帮助.

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