单元测试新手--如何使用Jest测试来测试这段代码？

Question

我是单元测试的新手。我想学习如何正确地使用Jest进行测试，在阅读了关于Udemy的文章、演示和课程之后，我仍然很困惑(尤其是使用Jest mocking)。我应该提一下，我们所有的代码都是在react之外的，所以它似乎更让我困惑。

我已经为我的公司写了一个AB测试，并且已经意识到它应该很容易测试，但我认为我做得不对。看起来我只是在复制我的原始代码来测试，尽管我觉得这个函数是有效的，但在我看来这似乎是错误的。

这是我正在讨论的代码和测试。你们这些更有经验的人怎么才能做到这一点呢？

谢谢!

JS：

let ABTestValue = 30;
ABTest();

export function ABTest() {
  const roll = Math.floor(Math.random() * 100);

  if (debugMode) {
    console.log('TimedRefresh - AB Test Issue-831 (90 and above get their refresh time changed) randomized value = ', roll);
  }

  const ABTestMappings = [
    {
      roll: 90,
      ABTestValue: 40
    },
    {
      roll: 91,
      ABTestValue: 40
    },
    {
      roll: 92,
      ABTestValue: 50
    },
    {
      roll: 93,
      ABTestValue: 50
    },
    {
      roll: 94,
      ABTestValue: 60
    },
    {
      roll: 95,
      ABTestValue: 60
    },
    {
      roll: 96,
      ABTestValue: 70
    },
    {
      roll: 97,
      ABTestValue: 70
    },
    {
      roll: 98,
      ABTestValue: 80
    },
    {
      roll: 99,
      ABTestValue: 80
    }
  ];

  if (roll > 89 && roll < 100) {
    ABTestValue = ABTestMappings.filter((a) => a.roll === roll)[0].ABTestValue;
  }

  window.rg_version = `time${ABTestValue}`;

  if (debugMode) {
    console.log('TimedRefresh - ABTestValue - change in refresh time in seconds (30 is default) - ', ABTestValue);
  }
}

test.js：

import { ABTest } from './index';

describe('ABTEST test', () => {
  it('ABTest function', () => {
    expect(ABTest).toBeDefined();
  })

  describe('test different rolls', () => {
    const ABTestMappings = [
      {
        roll: 90,
        ABTestValue: 40
      },
      {
        roll: 91,
        ABTestValue: 40
      },
      {
        roll: 92,
        ABTestValue: 50
      },
      {
        roll: 93,
        ABTestValue: 50
      },
      {
        roll: 94,
        ABTestValue: 60
      },
      {
        roll: 95,
        ABTestValue: 60
      },
      {
        roll: 96,
        ABTestValue: 70
      },
      {
        roll: 97,
        ABTestValue: 70
      },
      {
        roll: 98,
        ABTestValue: 80
      },
      {
        roll: 99,
        ABTestValue: 80
      }
    ];

    const roll = 92;
    const roll2 = 95;
    const roll3 = 99;
    const roll4 = 80;
    let ABTestValue = 30;
    let ABTestValue2 = 30;
    let ABTestValue3 = 30;
    let ABTestValue4 = 30;

    if (roll > 89 && roll < 100) {
      ABTestValue = ABTestMappings.filter((a) => a.roll === roll)[0].ABTestValue;
    }

    if (roll2 > 89 && roll2 < 100) {
      ABTestValue2 = ABTestMappings.filter((a) => a.roll === roll2)[0].ABTestValue;
    }

    if (roll3 > 89 && roll3 < 100) {
      ABTestValue3 = ABTestMappings.filter((a) => a.roll === roll3)[0].ABTestValue;
    }

    if (roll4 > 89 && roll4 < 100) {
      ABTestValue4 = ABTestMappings.filter((a) => a.roll === roll4)[0].ABTestValue;
    }

    it('if roll is 92', () => {
      if (roll) {
        expect(ABTestValue).toEqual(50);
      }
    })

    it('if roll is 95', () => {
      if (roll2) {
        expect(ABTestValue2).toEqual(60);
      }
    })

    it('if roll is 99', () => {
      if (roll3) {
        expect(ABTestValue3).toEqual(80);
      }
    })

    it('if roll is less than 90', () => {
      if (roll4) {
        expect(ABTestValue4).toEqual(30);
      }
    })
  })
})

Answer 1

单元测试工作流程非常简单。

1. 为要测试的方法/函数模拟依赖项及其返回值。为它创建一个隔离的环境。原则是单元测试不应该依赖于任何外部服务，例如发送一个真实的HTTP请求，查询真实的数据库，访问真实的文件system.
2. Execute你想要测试的方法/函数，测试每个分支(if...else，switch...case)，语句，函数和行。它们是覆盖率的总结，report.
3. Assert(expect)，结果，以及被测试的方法/函数所依赖的方法/函数是否要被调用。为什么？因为我们应该确保代码按照我们期望的

执行

在每个软件arch层中，按照上面的工作流程测试每个方法/函数。

软件架构层是指，例如，数据访问层、模型层、服务层、控制器/路由器层

下面是正确的单元测试：

index.ts

(window as any).rg_version = '';

export function ABTest(debugMode = false) {
  const roll = Math.floor(Math.random() * 100);
  let ABTestValue = 30;

  if (debugMode) {
    console.log(
      'TimedRefresh - AB Test Issue-831 (90 and above get their refresh time changed) randomized value = ',
      roll
    );
  }

  const ABTestMappings = [
    {
      roll: 90,
      ABTestValue: 40
    },
    {
      roll: 91,
      ABTestValue: 40
    },
    {
      roll: 92,
      ABTestValue: 50
    },
    {
      roll: 93,
      ABTestValue: 50
    },
    {
      roll: 94,
      ABTestValue: 60
    },
    {
      roll: 95,
      ABTestValue: 60
    },
    {
      roll: 96,
      ABTestValue: 70
    },
    {
      roll: 97,
      ABTestValue: 70
    },
    {
      roll: 98,
      ABTestValue: 80
    },
    {
      roll: 99,
      ABTestValue: 80
    }
  ];

  if (roll > 89 && roll < 100) {
    ABTestValue = ABTestMappings.filter(a => a.roll === roll)[0].ABTestValue;
  }

  (window as any).rg_version = `time${ABTestValue}`;

  if (debugMode) {
    console.log('TimedRefresh - ABTestValue - change in refresh time in seconds (30 is default) - ', ABTestValue);
  }
}

index.spec.ts

import { ABTest } from './';

describe('ABTest', () => {
  afterEach(() => {
    jest.restoreAllMocks();
    (window as any).rg_version = '';
  });
  it('should filter and get the correct value', () => {
    const floorSpy = jest.spyOn(Math, 'floor').mockReturnValueOnce(90);
    const logSpy = jest.spyOn(console, 'log');
    ABTest();
    expect((window as any).rg_version).toBe('time40');
    expect(floorSpy).toBeCalledTimes(1);
    expect(logSpy).toBeCalledTimes(0);
  });

  it('should get default value', () => {
    const floorSpy = jest.spyOn(Math, 'floor').mockReturnValueOnce(80);
    const logSpy = jest.spyOn(console, 'log');
    ABTest(true);
    expect((window as any).rg_version).toBe('time30');
    expect(floorSpy).toBeCalledTimes(1);
    expect(logSpy.mock.calls[0]).toEqual([
      'TimedRefresh - AB Test Issue-831 (90 and above get their refresh time changed) randomized value = ',
      80
    ]);
    expect(logSpy.mock.calls[1]).toEqual([
      'TimedRefresh - ABTestValue - change in refresh time in seconds (30 is default) - ',
      30
    ]);
  });
});

100%覆盖率的单元测试结果：

 PASS  src/stackoverflow/58258206/index.spec.ts
  ABTest
    ✓ should filter and get the correct value (8ms)
    ✓ should get default value (6ms)

  console.log node_modules/jest-mock/build/index.js:860
    TimedRefresh - AB Test Issue-831 (90 and above get their refresh time changed) randomized value =  80

  console.log node_modules/jest-mock/build/index.js:860
    TimedRefresh - ABTestValue - change in refresh time in seconds (30 is default) -  30

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 index.ts |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        2.814s, estimated 6s

源代码：https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/58258206