在Jest不起作用的情况下监视链接方法调用 [英] Spying on chained method calls with Jest not working

问题描述

我已经制作了自己的自定义TextInput组件，该组件带有nextField道具.当按下我的TextInput中的完成"按钮时，应将nextField对准焦点.很简单它可以在生产中使用.

I've made my own custom TextInput component that takes a nextField prop. When the "done" button in my TextInput is pressed, the nextField should be focused. Pretty simple. It works in production.

但是，我在测试聚焦nextField的代码行时遇到了麻烦:

However, I'm having trouble testing the line of code that focuses nextField:

this.props.nextField && this.props.nextField().focus()

我正在使用此间谍对其进行测试:

I'm testing it using this spy:

const nextFieldSpy = jest.fn(() => {return {focus: jest.fn()}})

据我了解，当触发测试中的代码行时，我应该看到同时调用了nextFieldSpy和nextFieldSpy().focus.

It's my understanding that when the line of code under test is triggered, I should see that nextFieldSpy and nextFieldSpy().focus have both been called.

但是，事实并非如此.这是开玩笑的期望:

However, this is not the case. Here are the Jest expectations:

expect(nextFieldSpy).toHaveBeenCalledTimes(1) expect(nextFieldSpy().focus).toHaveBeenCalledTimes(1)

这是我得到的错误-第一行通过，但第二行失败.

And this is the error I'm getting––the first line passes, but the second fails.

 Expected mock function to have been called one time, but it was called zero times.

  72 |     expect(nextFieldSpy).toHaveBeenCalledTimes(1)
> 73 |     expect(nextFieldSpy().focus).toHaveBeenCalledTimes(1)

这是怎么回事?

推荐答案

nextFieldSpy()每次调用时都会返回一个新对象.

nextFieldSpy() returns a new object every time it is called.

更改创建nextFieldSpy的方式以始终返回同一对象:

Change how you create nextFieldSpy to always return the same object:

const nextFieldResult = {focus: jest.fn()};
const nextFieldSpy = jest.fn(() => nextFieldResult);

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