Jest 单元测试 Singleton 类 Nodejs

Question

我在下面的代码中尝试对使用单例类的类变量的函数进行单元测试

单例类 a.js

class A{
constructor(){
   this.flag = true;
 }
 
setA(){
  this.flag=false;
  }
}

module.exports = new A(); //Singleton

使用单例类的类

import A from './a';

class B {
  constructor() {}

  hello() {
    if (A.flag) {
      console.log('1');
    } else {
      console.log('2');
    }
  }
}

b.test.js 的单元测试用例

import A from './a' //Singleton class
import B from './'

describe('Test Hello', () => {
    const b= new B();
    
    beforeEach(() => {      
    });

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


    test('Test Hello', async () => {        
        try{
            jest.spyOn(A, 'flag')
                .mockResolvedValueOnce(true);
            let output = b.hello();
                    
        }catch(e){
            console.log('Error', e);
        }
    });
});

所以 b.js 中的一行，console.log(1) 没有被覆盖在覆盖率报告中。尝试了多种选择

Answer 1

你的代码有很多问题：

1. 您正在测试b.js 模块，而不是a.js 模块。所以测试文件名应该是b.test.js。

2. 导入的模块名称错误。应该是./a.js，而不是A.js。

3. 如果要改变实例a的属性，只需要在测试用例中赋值即可

例如

a.js:

class A {
  constructor() {
    this.flag = true;
  }

  setA() {
    this.flag = false;
  }
}

module.exports = new A(); //Singleton

b.js:

import a from './a';

export class B {
  constructor() {}

  hello() {
    if (a.flag) {
      console.log('1');
    } else {
      console.log('2');
    }
  }
}

b.test.js:

import a from './a';
import { B } from './b';

describe('67335501', () => {
  afterEach(() => {
    jest.restoreAllMocks();
  });

  it('should print "1"', () => {
    const logSpy = jest.spyOn(console, 'log');
    a.flag = true;
    const b = new B();
    b.hello();
    expect(logSpy).toBeCalledWith('1');
  });

  it('should print "2"', () => {
    const logSpy = jest.spyOn(console, 'log');
    a.flag = false;
    const b = new B();
    b.hello();
    expect(logSpy).toBeCalledWith('2');
  });
});

单元测试结果：

 PASS  examples/67335501/b.test.js (10.808 s)
  67335501
    ✓ should print "1" (18 ms)
    ✓ should print "2" (2 ms)

  console.log
    1

      at console.<anonymous> (node_modules/jest-environment-enzyme/node_modules/jest-mock/build/index.js:866:25)

  console.log
    2

      at console.<anonymous> (node_modules/jest-environment-enzyme/node_modules/jest-mock/build/index.js:866:25)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |    87.5 |      100 |      75 |    87.5 |                   
 a.js     |   66.67 |      100 |      50 |   66.67 | 7                 
 b.js     |     100 |      100 |     100 |     100 |                   
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        12.657 s