在 Jest 中，如何模拟带有依赖项的 TypeScript 类？

Question

在 Jest 中，如何模拟带有依赖项的 TypeScript 类？

5

考虑到下面的这个比较繁琐的类获取Elasticsearch（或者其他数据存储方式）中的单个记录：

export default class UserRepoImpl implements UserRepo {
  constructor(private readonly esClient: ElasticsearchClient) {}

  public async getUser(id: string): Promise<User> {
    const response = await this.esClient.request('GET', `/users/_doc/${id}`);

    return response._source;
  }
}

我该如何编写一个测试，以便为我实例化一个UserRepoImpl，但在构造函数的参数中插入一个mocked ElasticsearchClient？

- Jeffrey Wen

2个回答

2

这里是单元测试解决方案： userRepoImpl.ts：

interface User {}
interface UserRepo {
  getUser(id: string): Promise<User>;
}
interface ElasticsearchClient {
  request(method: string, endpoint: string): Promise<{ _source: any }>;
}
export default class UserRepoImpl implements UserRepo {
  constructor(private readonly esClient: ElasticsearchClient) {}

  public async getUser(id: string): Promise<User> {
    const response = await this.esClient.request('GET', `/users/_doc/${id}`);

    return response._source;
  }
}

userRepoImpl.test.ts:

import UserRepoImpl from './userRepoImpl';

describe('62603645', () => {
  it('should pass', async () => {
    const mUser = { name: 'wen' };
    const mEsClient = { request: jest.fn().mockResolvedValueOnce({ _source: mUser }) };
    const userRepoImpl = new UserRepoImpl(mEsClient);
    const actual = await userRepoImpl.getUser('1');
    expect(actual).toEqual(mUser);
    expect(mEsClient.request).toBeCalledWith('GET', '/users/_doc/1');
  });
});

覆盖率报告的单元测试结果：

 PASS  stackoverflow/62603645/userRepoImpl.test.ts (10.988s)
  62603645
    ✓ should pass (5ms)

-----------------|---------|----------|---------|---------|-------------------
File             | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------------|---------|----------|---------|---------|-------------------
All files        |     100 |      100 |     100 |     100 |                   
 userRepoImpl.ts |     100 |      100 |     100 |     100 |                   
-----------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        12.27s

- Lin Du

我很欣赏你非常注重细节的解决方案。你知道你的变量mClient和teneff提供的solution`之间有什么区别吗？ - Jeffrey Wen

1

当我使用模拟客户端实例化新实例时，出现错误：

类型“{ request: Mock<any, any>; }”的参数无法分配给类型“ElasticsearchClient”。类型“{ request: Mock<any, any>; }”缺少类型“ElasticsearchClient”的以下属性：awsHttps、endpoint

。 - Jeffrey Wen

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- Teneff · Accepted Answer

你可以在测试中创建一个模拟客户端，就像这样：

您可以像这样在测试中创建模拟客户端：

const client: jest.Mocked<ElasticsearchClient> = {
  request: jest.fn()
}

这将在传递时对解析值的类型进行静态检查：

示例测试：

describe('UserRepoImpl', () => {
  describe('given a client', () => {
    const client: jest.Mocked<ElasticsearchClient> = {
      request: jest.fn()
    }
    describe('getUser', () => {
      beforeAll(() => {
        client.request.mockResolvedValue({
          _source: {
            id: '3'
          }
        })
      })

      it('should return user by Id', async () => {
        const userRepo = new UserRepoImpl(client)
        await expect(userRepo.getUser("3")).resolves.toEqual({
          id: '3'
        })
      })
    })
  })
})