Jasmine中如何模拟导入的类模块，替换MyModule的依赖实例？

首先先修正你代码中的几处语法错误，否则代码无法正常运行：

修正后的原文件 #

dependency.js #

function Dependency(property) {
    this.property = property;
}

Dependency.prototype.doSomething = function () {
    console.log('inside doSomething property: ', this.property);
}

export default Dependency;

myModule.js #

import Dependency from './Dependency.js';

function MyModule () {
   this.dependency = new Dependency('Some Property');
}

MyModule.prototype.init = function () {
    this.dependency.doSomething();
}

export default MyModule;

解决方案 #

方案一：依赖注入（推荐，代码更易测试） #

修改MyModule的构造函数，允许传入自定义的Dependency实例，测试时直接传入spy对象即可，无需mock模块：

修改后的myModule.js

import Dependency from './Dependency.js';

function MyModule (customDependency) {
   // 传入自定义实例则使用它，否则创建默认实例
   this.dependency = customDependency || new Dependency('Some Property');
}

MyModule.prototype.init = function () {
    this.dependency.doSomething();
}

export default MyModule;

测试文件myModule-test.js

import MyModule from '../myModule';
import Dependency from '../dependency';

describe('MyModule', () => {
  it('doSomething on the dependency called on init', () => {
    // 创建带有spy方法的假Dependency实例
    const dependencySpy = jasmine.createSpyObj('Dependency', ['doSomething']);
    
    // 传入假实例创建MyModule
    const myModule_ = new MyModule(dependencySpy);
    myModule_.init();

    // 验证spy方法被调用
    expect(dependencySpy.doSomething).toHaveBeenCalled();
  });
});

方案二：Mock模块的构造函数 #

如果不想修改原代码，可以通过Jasmine的spy功能，替换Dependency的构造行为，让new Dependency()返回假对象：

测试文件myModule-test.js

import MyModule from '../myModule';
import Dependency from '../dependency';

describe('MyModule', () => {
  it('doSomething on the dependency called on init', () => {
    // 创建带有spy方法的假实例
    const dependencySpy = jasmine.createSpyObj('Dependency', ['doSomething']);
    
    // 监视Dependency构造函数，让它返回假实例
    // 注意：如果是ES模块环境，需确保模块导出的Dependency可被替换，或挂载在全局对象上
    spyOn(window, 'Dependency').and.returnValue(dependencySpy);

    const myModule_ = new MyModule();
    myModule_.init();

    // 验证假实例的方法被调用
    expect(dependencySpy.doSomething).toHaveBeenCalled();
  });
});

若使用Node.js环境或Jest框架，可通过jest.mock更便捷地mock整个模块：

import MyModule from '../myModule';
import Dependency from '../dependency';

// Mock整个Dependency模块
jest.mock('../dependency', () => {
  return jest.fn().mockImplementation(() => {
    return { doSomething: jest.fn() };
  });
});

describe('MyModule', () => {
  it('doSomething on the dependency called on init', () => {
    const myModule_ = new MyModule();
    myModule_.init();

    // 获取构造出的假实例，验证方法被调用
    const mockDependencyInstance = Dependency.mock.instances[0];
    expect(mockDependencyInstance.doSomething).toHaveBeenCalled();
  });
});

内容的提问来源于stack exchange，提问作者3960278