如何在Jest中Mock NestJS的RabbitMQ模块？求解决方案

问题场景 #

现有AppModule代码如下：

import { Module } from '@nestjs/common'
import { RabbitMQModule } from '@golevelup/nestjs-rabbitmq'

@Module({
    imports: [
        RabbitMQModule.forRoot(RabbitMQModule, {
            exchanges: [
                {
                    name: 'my_rabbit',
                    type: 'direct',
                },
            ],
            uri: process.env.RABBITMQ_URI,
            connectionInitOptions: { wait: true },
        }),
    ],
})
export class AppModule {}

尝试两种Mock方式均失败：

方式一：覆盖AmqpConnection提供者 #

代码：

import { Module } from '@nestjs/common'
import { RabbitMQModule } from '@golevelup/nestjs-rabbitmq'

beforeEach(async () => {
        const module: TestingModule = await Test.createTestingModule({
            imports: [
                AppModule
            ],
        })
            .overrideProvider(AmqpConnection)
            .useValue(createMock<AmqpConnection>())
            .compile()
    })

报错：

[Nest] 2745  - 24/07/2022, 17:02:54   ERROR [AmqpConnection] Disconnected from RabbitMQ broker (default)
Error: connect ECONNREFUSED 127.0.0.1:5672

原因：RabbitMQModule.forRoot在模块初始化阶段就会尝试建立真实连接，overrideProvider的操作时机太晚，无法阻止连接请求。

方式二：直接Mock整个模块 #

代码：

jest.mock('@golevelup/nestjs-rabbitmq')

报错：

Nest cannot create the AppModule instance.
    The module at index [0] of the AppModule "imports" array is undefined.

原因：jest.mock会把模块的所有导出替换为undefined，导致RabbitMQModule.forRoot无法返回有效模块实例。

正确解决方案 #

方案1：Mock RabbitMQModule的forRoot方法 #

通过jest.mock自定义模块导出，让forRoot返回空Nest模块，同时MockAmqpConnection类：

import { Test } from '@nestjs/testing';
import { AppModule } from './app.module';
import { AmqpConnection } from '@golevelup/nestjs-rabbitmq';
import { createMock } from '@golevelup/ts-jest';

jest.mock('@golevelup/nestjs-rabbitmq', () => ({
  RabbitMQModule: {
    forRoot: jest.fn().mockReturnValue({
      module: class {},
    }),
  },
  AmqpConnection: jest.fn(),
}));

describe('AppModule', () => {
  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      imports: [AppModule],
    })
      .overrideProvider(AmqpConnection)
      .useValue(createMock<AmqpConnection>())
      .compile();
  });

  // 测试用例编写...
});

方案2：手动构建测试依赖，避免真实连接 #

直接在测试模块中导入业务模块，配合Mock配置的RabbitMQModule，跳过真实连接逻辑：

import { Test } from '@nestjs/testing';
import { RabbitMQModule } from '@golevelup/nestjs-rabbitmq';
import { createMock } from '@golevelup/ts-jest';
import { AmqpConnection } from '@golevelup/nestjs-rabbitmq';
import { YourService } from './your.service';

describe('YourService', () => {
  let service: YourService;
  let amqpConnection: jest.Mocked<AmqpConnection>;

  beforeEach(async () => {
    amqpConnection = createMock<AmqpConnection>();

    const module: TestingModule = await Test.createTestingModule({
      imports: [
        RabbitMQModule.forRoot(RabbitMQModule, {
          exchanges: [{ name: 'my_rabbit', type: 'direct' }],
          uri: 'amqp://guest:guest@localhost:5672',
          connectionInitOptions: { wait: false }, // 禁用连接等待
        }),
      ],
      providers: [YourService],
    })
      .overrideProvider(AmqpConnection)
      .useValue(amqpConnection)
      .compile();

    service = module.get<YourService>(YourService);
  });

  it('should trigger RabbitMQ publish', () => {
    service.sendTestMessage();
    expect(amqpConnection.publish).toHaveBeenCalled();
  });
});

方案3：用overrideModule替换原RabbitMQModule #

若要保留AppModule结构，可通过overrideModule替换掉原有的RabbitMQModule导入：

import { Test } from '@nestjs/testing';
import { AppModule } from './app.module';
import { RabbitMQModule } from '@golevelup/nestjs-rabbitmq';
import { createMock } from '@golevelup/ts-jest';
import { AmqpConnection } from '@golevelup/nestjs-rabbitmq';

describe('AppModule', () => {
  beforeEach(async () => {
    const mockRabbitModule = RabbitMQModule.forRoot(RabbitMQModule, {
      exchanges: [{ name: 'my_rabbit', type: 'direct' }],
      uri: 'amqp://mock:mock@localhost:5672',
      connectionInitOptions: { wait: false },
    });

    const module: TestingModule = await Test.createTestingModule({
      imports: [AppModule],
    })
      .overrideModule(RabbitMQModule)
      .useModule(mockRabbitModule)
      .overrideProvider(AmqpConnection)
      .useValue(createMock<AmqpConnection>())
      .compile();
  });
});

内容的提问来源于stack exchange，提问作者Calvintwr