如何在玩笑中模拟/监视 useState 钩子？

Question

我试图监视 useState React 钩子，但我总是测试失败

这是我的 React 组件：

const Counter= () => {
    const[counter, setCounter] = useState(0);

    const handleClick=() => {
        setCounter(counter + 1);
    }

    return (
        <div>
            <h2>{counter}</h2>
            <button onClick={handleClick} id="button">increment</button>
        </div>
    )
}

counter.test.js：

it('increment counter correctlry', () => {
    let wrapper = shallow(<Counter/>);
    const setState = jest.fn();
    const useStateSpy = jest.spyOn(React, 'useState');

    useStateSpy.mockImplementation((init) => [init, setState]);
     const button = wrapper.find("button")
     button.simulate('click');
     expect(setState).toHaveBeenCalledWith(1);
})

不幸的是，这不起作用，我得到了测试失败的消息：

expected 1
Number of calls: 0

Answer 1

您需要使用React.useState 而不是单一导入useState。

我认为是关于代码如何获取 transpiled，正如您在 babel repl 中看到的那样，来自单个导入的 useState 最终与模块导入中的一个不同

_react.useState // useState
_react.default.useState // React.useState;

所以你监视_react.default.useState，但你的组件使用_react.useState。 似乎不可能监视单个导入，因为您需要该函数属于一个对象，这是一个非常广泛的指南，解释了模拟/监视模块的方式https://github.com/HugoDF/mock-spy-module-import

正如@Alex Mackay 提到的，你可能想改变你对测试反应组件的心态，建议转向反应测试库，但如果你真的需要坚持使用酶，你不需要走那么远至于模拟反应库本身

Answer 2

diedu 的回答让我找到了正确的方向，我想出了这个解决方案：

1. 从 react 中模拟使用状态以返回 jest.fn() 作为 useState： 1.1 同样在之后立即导入 useState - 现在将是 e jest mock（从 jest.fn() 调用返回）

jest.mock('react', ()=>({
  ...jest.requireActual('react'),
  useState: jest.fn()
}))
import { useState } from 'react';

1. 稍后在 beforeEach 中，将其设置为原始 useState，以便在所有需要它不被模拟的情况下

describe("Test", ()=>{
  beforeEach(()=>{
    useState.mockImplementation(jest.requireActual('react').useState);
    //other preperations
  })
  //tests
})

1. 在测试本身中根据需要对其进行模拟：

it("Actual test", ()=>{
  useState.mockImplementation(()=>["someMockedValue", someMockOrSpySetter])
})

临别笔记：虽然在“黑匣子”中弄脏你的手在概念上可能有些错误，其中之一是单元测试，但有时这样做确实非常有用。

Answer 3

令人讨厌的是 Codesandbox 目前的测试模块有问题，所以我无法发布一个工作示例，但我会尝试解释为什么模拟 useState 通常是一件坏事。

用户不关心是否调用了useState，他们关心的是当我单击递增时，计数应该增加一，因此这就是您应该测试的内容。

// App
import React, { useState } from "react";
export default function App() {
  const [count, setCount] = useState(0);
  return (
    <div>
      <h1>Count: {count}</h1>
      <button onClick={() => setCount((prev) => prev + 1)}>Increment</button>
    </div>
  );
}
// Tests
import React from "react";
import App from "./App";
import { screen, render } from "@testing-library/react";
import userEvent from "@testing-library/user-event";

describe("App should", () => {
  it('increment count value when "Increment" btn clicked', () => {
    // Render the App
    render(<App />);
    // Get the count in the same way the user would, by looking for 'Count'
    let count = screen.getByText(/count:/);
    // As long as the h1 element contains a '0' this test will pass
    expect(count).toContain(0);
    // Once again get the button in the same the user would, by the 'Increment'
    const button = screen.getByText(/increment/);
    // Simulate the click event
    userEvent.click(button);
    // Refetch the count
    count = screen.getByText(/count:/);
    // The 'Count' should no longer contain a '0'
    expect(count).not.toContain(0);
    // The 'Count' should contain a '1'
    expect(count).toContain(1);
  });
  // And so on...
  it('reset count value when "Reset" btn is clicked', () => {});
  it('decrement count value when "Decrement" btn is clicked', () => {});
});

如果您对这种测试方式感兴趣，请务必查看@testing-library。大约 2 年前，我从 enzyme 切换过来，从那以后就再也没碰过它。

Answer 4

只需要在测试文件中导入 React，例如：

import * as React from 'react';

之后就可以使用mock函数了。

import * as React from 'react';

:
:
it('increment counter correctlry', () => {
    let wrapper = shallow(<Counter/>);
    const setState = jest.fn();
    const useStateSpy = jest.spyOn(React, 'useState');

    useStateSpy.mockImplementation((init) => [init, setState]);
     const button = wrapper.find("button")
     button.simulate('click');
     expect(setState).toHaveBeenCalledWith(1);
})

Answer 5

你应该使用 React.useState() 而不是 useState()，但是还有其他方法... 在 React 中，您可以使用此配置设置 useState 而不使用 React

// setupTests.js
    const { configure } = require('enzyme')
    const Adapter = require('@wojtekmaj/enzyme-adapter-react-17')
    const { createSerializer } = require('enzyme-to-json')

    configure({ adapter: new Adapter() });
    expect.addSnapshotSerializer(createSerializer({
        ignoreDefaultProps: true,
        mode: 'deep',
        noKey: true,
    }));

import React, { useState } from "react";

    const Home = () => {

        const [count, setCount] = useState(0);

        return (
            <section>

                <h3>{count}</h3>
                <span>
                    <button id="count-up" type="button" onClick={() => setCount(count + 1)}>Count Up</button>
                    <button id="count-down" type="button" onClick={() => setCount(count - 1)}>Count Down</button>
                    <button id="zero-count" type="button" onClick={() => setCount(0)}>Zero</button>
                </span>
            </section>
        );

    }

    export default Home;

// index.test.js

    import { mount } from 'enzyme';
    import Home from '../';
    import React, { useState as useStateMock } from 'react';


    jest.mock('react', () => ({
        ...jest.requireActual('react'),
        useState: jest.fn(),
    }));

    describe('<Home />', () => {
        let wrapper;

        const setState = jest.fn();

        beforeEach(() => {
            useStateMock.mockImplementation(init => [init, setState]);
            wrapper = mount(<Home />);
        });

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

        describe('Count Up', () => {
            it('calls setCount with count + 1', () => {
                wrapper.find('#count-up').simulate('click');
                expect(setState).toHaveBeenCalledWith(1);
            });
        });

        describe('Count Down', () => {
            it('calls setCount with count - 1', () => {
                wrapper.find('#count-down').props().onClick();
                expect(setState).toHaveBeenCalledWith(-1);
            });
        });

        describe('Zero', () => {
            it('calls setCount with 0', () => {
                wrapper.find('#zero-count').props().onClick();
                expect(setState).toHaveBeenCalledWith(0);
            });
        });
    });