如何用Jest测试含依赖的函数？Mock类型不匹配问题求解

需要测试以下函数：

export const Update = (factory: Factory, service: MyService) => {
  return async (input: Input) => {
    return factory.transaction(async (fact) => {
      const someValues = myService.getSomeValues()
      return fact.findAll(someValues, input)
    }
  }
}

测试时尝试传入Mock的Factory类及MyService，但出现类型不匹配错误，测试代码如下：

import Factory from 'factory'
jest.mock('factory')
const mockedFactory = jest.mocked(Factory)
const expectedUpdate = Update(mockedFactory)

错误信息：

Argument of type 'MockedObject' is not assignable to parameter of type 'Factory'. Type 'MockInstance<Factory,
[sequelize: Sequelize]> & {} & { prototype: Factory; }' is missing the
following properties from type 'Factory': sequelize, transaction

需要解决类型错误，同时验证Factory的transaction方法、MyService的getSomeValues方法调用情况，以及fact.findAll的参数和Update函数的返回结果。

1. 修正Factory的Mock方式，解决类型不匹配 #

问题核心是jest.mocked(Factory)拿到的是类的构造函数Mock，而非符合Factory类型的实例对象。需要手动构造或Mock出包含必要属性的实例：

方式一：手动构造符合Factory类型的Mock对象 #

// 模拟transaction方法，确保执行回调并传入mock的fact对象
const mockTransaction = jest.fn(async (callback) => {
  const mockFact = {
    findAll: jest.fn().mockResolvedValue('mock-result')
  };
  return callback(mockFact);
});

// 构造符合Factory类型的mock对象，用类型断言处理sequelize属性
const mockedFactory: Factory = {
  sequelize: {} as Sequelize,
  transaction: mockTransaction
};

// Mock MyService对象
const myServiceMock = {
  getSomeValues: jest.fn().mockReturnValue('mock-some-values')
};

// 现在传入不会有类型错误
const updateFunction = Update(mockedFactory, myServiceMock);

方式二：Mock可实例化的Factory类 #

如果Factory是需要实例化的类，直接Mock类的实例方法：

import Factory from 'factory';

jest.mock('factory', () => {
  return jest.fn().mockImplementation(() => {
    return {
      sequelize: {} as Sequelize,
      transaction: jest.fn(async (callback) => {
        const mockFact = { findAll: jest.fn().mockResolvedValue('mock-result') };
        return callback(mockFact);
      })
    };
  });
});

// 创建Mock实例
const mockedFactoryInstance = new Factory();
const myServiceMock = { getSomeValues: jest.fn().mockReturnValue('mock-some-values') };
const updateFunction = Update(mockedFactoryInstance, myServiceMock);

2. 验证函数调用、参数及返回结果 #

完成Mock后，编写测试用例验证各个环节：

describe('Update function', () => {
  it('should verify all method calls and results', async () => {
    const testInput = { id: 1 };
    
    // 执行Update返回的异步函数
    const result = await updateFunction(testInput);

    // 验证Factory.transaction被调用
    expect(mockedFactory.transaction).toHaveBeenCalledTimes(1);
    
    // 验证MyService.getSomeValues被调用
    expect(myServiceMock.getSomeValues).toHaveBeenCalledTimes(1);
    
    // 获取transaction回调中的mockFact，验证findAll的参数
    const transactionCallback = mockedFactory.transaction.mock.calls[0][0];
    const mockFact = await transactionCallback(jest.fn());
    expect(mockFact.findAll).toHaveBeenCalledWith('mock-some-values', testInput);
    
    // 验证Update函数的返回结果
    expect(result).toBe('mock-result');
  });
});

关键说明 #

• 类型错误的本质是传入的Mock对象不符合Factory类型要求，必须包含sequelize和transaction属性。
• Mocktransaction时必须执行传入的回调函数，否则内部的fact.findAll不会触发。
• 用mockResolvedValue模拟异步函数的返回值，确保测试用例能正确等待异步操作完成。

内容的提问来源于stack exchange，提问作者Gigabit