NestJS单元测试中注入HttpService失败问题排查

问题场景 #

我编写了依赖HttpService的SimpleService：

import { Injectable } from '@nestjs/common';
import { HttpService } from '@nestjs/axios';

@Injectable()
export class SimpleService {
  constructor(private readonly httpService: HttpService) {}
  method() {
    console.log('Hello World!');
  }
}

对应的单元测试代码：

import { Test } from '@nestjs/testing';
import { HttpService } from '@nestjs/axios';
import { SimpleService } from './test.service';

describe('test SimpleService', () => {
  let simpleService: SimpleService;
  let httpService: HttpService;

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [
        {
          provide: HttpService,
          useValue: {
            get: jest.fn(),
          },
        },
        SimpleService,
      ],
    }).compile();

    simpleService = module.get<SimpleService>(SimpleService);
    httpService = module.get<HttpService>(HttpService);
  });

  it('should be defined', () => {
    expect(httpService).toBeDefined();
    expect(simpleService).toBeDefined();
  });
});

运行测试时出现错误：

Error: Nest can't resolve dependencies of the SimpleService (?). Please make sure that the argument dependency at index [0] is available in the RootTestModule context.

问题原因 #

@nestjs/axios中的HttpService并非直接以类作为注入令牌，Nest内部使用了特定的令牌（HTTP_SERVICE常量）来标识这个服务，直接用HttpService类作为provide的值无法被Nest识别，导致依赖解析失败。

解决方法 #

方法一：使用正确的注入令牌 #

从@nestjs/axios导入HTTP_SERVICE常量，替换测试模块中的provide值：

import { Test } from '@nestjs/testing';
import { HttpService, HTTP_SERVICE } from '@nestjs/axios';
import { SimpleService } from './test.service';

describe('test SimpleService', () => {
  let simpleService: SimpleService;
  let httpService: HttpService;

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [
        {
          provide: HTTP_SERVICE,
          useValue: {
            get: jest.fn(),
          },
        },
        SimpleService,
      ],
    }).compile();

    simpleService = module.get<SimpleService>(SimpleService);
    httpService = module.get<HttpService>(HTTP_SERVICE);
  });

  it('should be defined', () => {
    expect(httpService).toBeDefined();
    expect(simpleService).toBeDefined();
  });
});

方法二：Mock整个@nestjs/axios模块 #

通过jest.mock直接模拟整个模块，让Nest能正确识别HttpService类：

jest.mock('@nestjs/axios', () => ({
  HttpService: jest.fn(() => ({
    get: jest.fn(),
  })),
}));

import { Test } from '@nestjs/testing';
import { HttpService } from '@nestjs/axios';
import { SimpleService } from './test.service';

describe('test SimpleService', () => {
  let simpleService: SimpleService;
  let httpService: HttpService;

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [SimpleService, HttpService],
    }).compile();

    simpleService = module.get<SimpleService>(SimpleService);
    httpService = module.get<HttpService>(HttpService);
  });

  it('should be defined', () => {
    expect(httpService).toBeDefined();
    expect(simpleService).toBeDefined();
  });
});

内容的提问来源于stack exchange，提问作者Jamshoot