开玩笑 - 如何模拟模块使用的类？答案

【问题标题】：Jest - how to mock a Class used by a module?开玩笑 - 如何模拟模块使用的类？
【发布时间】：2020-03-24 23:06:22
【问题描述】：

我有课：

class RequestTimeout {
    constructor(timeoutMilliseconds) {
        this.timeoutMilliseconds = timeoutMilliseconds;
        this.timeoutID = undefined;
    }

    start() {
        return new Promise((resolve, reject) => {
            this.timeoutID = setTimeout(() => reject(new Error(`Request attempt exceeded timeout of ${this.timeoutMilliseconds}`)), this.timeoutMilliseconds);
        });
    }

    clear() {
        if (this.timeoutID) clearTimeout(this.timeoutID);
    }
}

module.exports = RequestTimeout;

这个类在一个模块中使用：

const RequestTimeout = require('./request-timeout');

function Request() {
  ...

  async function withTimeout(request, ms) {
        const timeout = new RequestTimeout(ms);

        return Promise.race([
            request(),
            timeout.start(),
        ])
            .then(
                response => {
                    timeout.clear();
                    return response;
                },
                err => {
                    timeout.clear();
                    throw err;
                }
            );
    }

  ...
}

如何在使用Request 的测试中模拟RequestTimeout？例如：

it('should clear the timeout following a successful response', async () => {
  nock('http://example.com')
    .get('/')
    .reply(200, { example: true });

  const response = await request.get({ ...baseOptions });

  expect(response.example).toEqual(true);
});

【问题讨论】：

标签： jestjs

【解决方案1】：

// 模拟

let mockGetTimeOutId = jest.fn();
jest.mock('../request-timeout', () => {
    return jest.fn().mockImplementation((ms) => {
        let timeoutId = undefined;
        return {
            start: () => new Promise((resolve, reject) => {
                timeoutId = setTimeout(() => reject(), ms);
            }),
            clear: () => mockGetTimeOutId(timeoutId),
        }
    })
});

// 测试

it('should clear the timeout following a successful response', async () => {
    nock('http://example.com')
        .get('/')
        .reply(200, { example: true });

    expect(mockGetTimeOutId).toHaveBeenCalledTimes(0);

    const response = await request.get({ ...baseOptions });

    expect(mockGetTimeOutId).toHaveBeenCalledTimes(1);
    expect(response.example).toEqual(true);
});

【讨论】：