Jest - 在打字稿中模拟一个命名的类导出

Question

我有一个导出几个类的节点模块，其中一个是Client，我用它来创建一个客户端（有几个 API 作为方法）。

我正在尝试使用 Jest 测试我的模块，该模块将此节点模块用作依赖项。但是，我无法成功模拟 Client 类中的一种方法（比如 search()）。

这是我对myModule 的规范：

//index.spec.ts
import * as nock from 'nock';
import * as externalModule from 'node-module-name';
import { createClient } from './../../src/myModule';
describe(() => {
  beforeAll(() => {
    nock.disableNetConnect();
  });
  it('test search method in my module', () => {
    jest.mock('node-module-name');

    const mockedClient = <jest.Mock<externalModule.Client>>externalModule.Client;

    const myClient = createClient({/*params*/}); //returns instance of Client class present in node module by executing Client() constructor
    myClient.searchByName('abc'); //calls search API - I need to track calls to this API

    expect(mockedClient).toHaveBeenCalled();
    expect(mockedClient.prototype.search).toHaveBeenCalledWith('abc');
  });
});

然而，这根本不会创建模拟，并会触发一个 nock 错误，因为搜索 API 会尝试连接到 url（通过参数给出）。

我也尝试过像下面这样模拟 Client 类。虽然成功地为 Client 类和搜索 API 创建了一个模拟（验证 search() 也通过控制台日志模拟），但当我尝试检查是否已调用 search() 时，它给了我一个错误。

externalModule.Client = jest.fn(() => { return { search: jest.fn(() => Promise.resolve('some response')) } });
//creates the mock successfully, but not sure how to track calls to 'search' property

const client = myModule.createClient(/*params*/);
client.searchByName('abc');

expect(externalModule.Client).toHaveBeenCalled(); //Successful
expect(externalModule.Client.prototype.search).toHaveBeenCalled(); //returns error saying "jest.fn() value must be a mock function or spy, Received: undefined"

我不确定我做错了什么。提前谢谢你。

Answer 1

模拟整个模块

尝试将jest.mock 移动到文件顶部

//index.spec.ts
const search = jest.fn();
jest.mock('node-module-name', () => ({
  Client: jest.fn(() => ({ search }))
}));
import * as nock from 'nock';
import * as externalModule from 'node-module-name';
import { createClient } from './../../src/myModule';
describe(() => {
  beforeAll(() => {
    nock.disableNetConnect();
  });
  it('test search method in my module', () => {
    const myClient = createClient({/*params*/});
    myClient.searchByName('abc'); 

    expect(externalModule.Client).toHaveBeenCalled();
    expect(search).toHaveBeenCalledWith('abc');
    externalModule.Client.mockClear();
    search.mockClear();
  });
});

仅模拟客户端

创建search 常量并跟踪它。

const search = jest.fn();
externalModule.Client = jest.fn(() => ({ search }));

const client = myModule.createClient(/*params*/);
client.searchByName('abc');

expect(externalModule.Client).toHaveBeenCalled();
expect(search).toHaveBeenCalled();

Answer 2

这就是我嘲笑它的方式。我不得不更改命名并删除一些代码以避免暴露原始源代码。

jest.mock('../foo-client', () => {
  return { FooClient: () => ({ post: mockPost }) }
})

完整代码。

// foo-client.ts

export class FooClient {
    constructor(private config: any)
    post() {}
}

// foo-service.ts

import { FooClient } from './foo-client'

export class FooLabelService {
    private client: FooClient
    constructor() {
        this.client = new FooClient()
    }

    createPost() {
        return this.client.post()
    }
}

// foo-service-test.ts

import { FooService } from '../foo-service'

const mockPost = jest.fn()
jest.mock('../foo-client', () => {
  return { FooClient: () => ({ post: mockPost }) }
})

describe('FooService', () => {
  let fooService: FooService

  beforeEach(() => {
    jest.resetAllMocks()
    fooService = new FooService()
  })

  it('something should happened', () => {
    mockPost.mockResolvedValue()
    fooService.createPost()
  })
})