去抖功能的开玩笑单元测试

Question

我正在尝试为 debounce 函数编写单元测试。想都想不起来了

这是代码：

function debouncer(func, wait, immediate) {
  let timeout;

  return (...args) => {
    clearTimeout(timeout);

    timeout = setTimeout(() => {
      timeout = null;
      if (!immediate) 
        func.apply(this, args);
    }, wait);

    if (immediate && !timeout) 
      func.apply(this, args);
  };
}

我应该如何开始？

Answer 1

您可能想要检查去抖函数中的逻辑：

timeout 将始终由最后一个 if() 语句设置
this 将始终是 undefined，因为 arrow functions use "the this value of the enclosing lexical context" 和 debouncer() 旨在用作独立函数。

话虽如此，听起来您真正的问题是关于测试去抖功能。

测试去抖函数

您可以通过使用 mock 来跟踪函数调用并使用假计时器来模拟时间的流逝来测试函数是否已去抖动。

这是一个使用 Jest Mock Function and Sinon fake timers of a function debounced using debounce() from Lodash:

的简单示例

const _ = require('lodash');
import * as sinon from 'sinon';

let clock;

beforeEach(() => {
  clock = sinon.useFakeTimers();
});

afterEach(() => {
  clock.restore();
});

test('debounce', () => {
  const func = jest.fn();
  const debouncedFunc = _.debounce(func, 1000);

  // Call it immediately
  debouncedFunc();
  expect(func).toHaveBeenCalledTimes(0); // func not called

  // Call it several times with 500ms between each call
  for(let i = 0; i < 10; i++) {
    clock.tick(500);
    debouncedFunc();
  }
  expect(func).toHaveBeenCalledTimes(0); // func not called

  // wait 1000ms
  clock.tick(1000);
  expect(func).toHaveBeenCalledTimes(1);  // func called
});

Answer 2

实际上，您不需要使用 Sinon 来测试去抖动。 Jest 可以模拟 JavaScript 代码中的所有计时器。

查看以下代码（它是 TypeScript，但您可以轻松地将其转换为 JavaScript）：

import * as _ from 'lodash';

// Tell Jest to mock all timeout functions
jest.useFakeTimers();

describe('debounce', () => {

    let func: jest.Mock;
    let debouncedFunc: Function;

    beforeEach(() => {
        func = jest.fn();
        debouncedFunc = _.debounce(func, 1000);
    });

    test('execute just once', () => {
        for (let i = 0; i < 100; i++) {
            debouncedFunc();
        }

        // Fast-forward time
        jest.runAllTimers();

        expect(func).toBeCalledTimes(1);
    });
});

更多信息：Timer Mocks

Answer 3

如果在您的代码中这样做：

import debounce from 'lodash/debounce';

myFunc = debounce(myFunc, 300);

并且您想测试函数 myFunc 或调用它的函数，那么在您的测试中，您可以使用 jest 模拟 debounce 的实现，使其只是 return 你的函数：

import debounce from 'lodash/debounce';

// Tell Jest to mock this import
jest.mock('lodash/debounce');

it('my test', () => {
    // ...
    debounce.mockImplementation(fn => fn); // Assign the import a new implementation. In this case it's to execute the function given to you
    // ...
});

来源：https://gist.github.com/apieceofbart/d28690d52c46848c39d904ce8968bb27

Answer 4

我喜欢这个类似的版本更容易失败：

jest.useFakeTimers();
test('execute just once', () => {
    const func = jest.fn();
    const debouncedFunc = debounce(func, 500);

    // Execute for the first time
    debouncedFunc();

    // Move on the timer
    jest.advanceTimersByTime(250);
    // try to execute a 2nd time
    debouncedFunc();

    // Fast-forward time
    jest.runAllTimers();

    expect(func).toBeCalledTimes(1);
});

Answer 5

另一种方法是刷新去抖功能，让它立即执行：

test('execute just once', () => {
    const func = jest.fn();
    const debouncedFunc = debounce(func, 500);

    // Execute for the first time
    debouncedFunc();
    debouncedFunc.flush();

  
    // try to execute a 2nd time
    debouncedFunc();
    debouncedFunc.flush();

    expect(func).toBeCalledTimes(1);
});

Answer 6

使用现代假定时器（Jest 27 已经默认）你可以更简洁地测试它：

import debounce from "lodash.debounce";
describe("debounce", () => {
  beforeEach(() => {
    jest.useFakeTimers("modern");
  });
  afterEach(() => {
    jest.useRealTimers();
  });
  it("should work properly", () => {
    const callback = jest.fn();
    const debounced = debounce(callback, 500);
    debounced();
    expect(callback).not.toBeCalled();

    jest.advanceTimersByTime(100);
    debounced();
    expect(callback).not.toBeCalled();

    jest.advanceTimersByTime(499);
    expect(callback).not.toBeCalled();

    jest.advanceTimersByTime(1);
    expect(callback).toBeCalledTimes(1);
  });

  it("should fire with lead", () => {
    const callback = jest.fn();
    const debounced = debounce(callback, 500, { leading: true });
    expect(callback).not.toBeCalled();
    debounced();
    expect(callback).toBeCalledTimes(1);

    jest.advanceTimersByTime(100);
    debounced();
    expect(callback).toBeCalledTimes(1);

    jest.advanceTimersByTime(499);
    expect(callback).toBeCalledTimes(1);

    jest.advanceTimersByTime(1);
    expect(callback).toBeCalledTimes(2);
  });
});

您可以将其实现为像这样去抖动的状态挂钩...

import debounce from "lodash.debounce";
import { Dispatch, useCallback, useState } from "react";

export function useDebouncedState<S>(
  initialValue: S,
  wait: number,
  debounceSettings?: Parameters<typeof debounce>[2]
): [S, Dispatch<S>] {
  const [state, setState] = useState<S>(initialValue);
  const debouncedSetState = useCallback(
    debounce(setState, wait, debounceSettings),
    [wait, debounceSettings]
  );
  return [state, debouncedSetState];
}

并测试为

/**
 * @jest-environment jsdom
 */
import { act, render, waitFor } from '@testing-library/react';
import React from 'react';
import { useDebouncedState } from "./useDebouncedState";

describe("useDebounceState", () => {
  beforeEach(() => {
    jest.useFakeTimers("modern");
  });
  afterEach(() => {
    jest.useRealTimers();
  });
  it("should work properly", async () => {
    const callback = jest.fn();
    let clickCount = 0;
    function MyComponent() {
      const [foo, setFoo] = useDebouncedState("bar", 500);
      callback();
      return <div data-testid="elem" onClick={() => { ++clickCount; setFoo("click " + clickCount); }}>{foo}</div>
    }
    const { getByTestId } = render(<MyComponent />)
    const elem = getByTestId("elem");

    expect(callback).toBeCalledTimes(1);
    expect(elem.textContent).toEqual("bar");

    jest.advanceTimersByTime(100);
    elem.click();
    expect(callback).toBeCalledTimes(1);
    expect(elem.textContent).toEqual("bar");

    jest.advanceTimersByTime(399);
    expect(callback).toBeCalledTimes(1);
    expect(elem.textContent).toEqual("bar");

    act(() => jest.advanceTimersByTime(1));

    await waitFor(() => {
      expect(callback).toBeCalledTimes(2);
      expect(elem.textContent).toEqual("click 1");
    });

    elem.click();
    await waitFor(() => {
      expect(callback).toBeCalledTimes(2);
      expect(elem.textContent).toEqual("click 1");
    });
    act(() => jest.advanceTimersByTime(500));
    await waitFor(() => {
      expect(callback).toBeCalledTimes(3);
      expect(elem.textContent).toEqual("click 2");
    });

  });
});

源代码位于 https://github.com/trajano/react-hooks-tests/tree/master/src/useDebouncedState

Answer 7

花了很多时间弄清楚...终于成功了..

jest.mock('lodash', () => {
    const module = jest.requireActual('lodash');
    module.debounce = jest.fn(fn => fn);
    return module;
});

Answer 8

这是我的 3 个基本测试：

有测试去抖动逻辑的基础。
请注意，所有测试都是 async 因为测试的本质本身就是异步的。

import debounce from 'lodash.debounce'

const wait = ms => new Promise(resolve => setTimeout(resolve, ms))

test('called repeatedly', async () => {
  const DELAY = 100;
  let callCount = 0;
  const debounced = debounce(() => ++callCount, DELAY)

  for( let i = 4; i--; )
    debounced()
 
  await delay(DELAY)
  expect( callCount ).toBe(1) 
})


test('called repeatedly exactly after the delay', async () => {
  const DELAY = 100;
  let callCount = 0, times = 3;
  const debounced = debounce(() => ++callCount, DELAY)

  for( let i = times; i--; ) {
    debounced()
    await delay(DELAY) 
  }
 
  await delay(DELAY * times)
  expect( callCount ).toBe(3) 
})


test('called repeatedly at an interval small than the delay', async () => {
  const DELAY = 100;
  let callCount = 0, times = 6;
  const debounced = debounce(() => ++callCount, DELAY)

  for( let i = times; i--; ) {
    debounced()
    await delay(DELAY/2) 
  }
 
  await delay(DELAY * times)
  expect( callCount ).toBe(1) 
})

这些测试是我写的，不是取自lodash debounce tests source code

去抖功能的开玩笑单元测试

Jest unit test for a debounce function

javascript

unit-testing

jestjs

debounce

测试去抖函数

这是我的 3 个基本测试：