用 Sinon.JS 模拟 JavaScript 构造函数

Question

我想对以下 ES6 类进行单元测试：

// service.js
const InternalService = require('internal-service');

class Service {
  constructor(args) {
    this.internalService = new InternalService(args);
  }

  getData(args) {   
    let events = this.internalService.getEvents(args);
    let data = getDataFromEvents(events);
    return data;
  }
}

function getDataFromEvents(events) {...}

module.exports = Service;

如何使用 Sinon.JS 模拟构造函数以模拟

getEvents

的

internalService

以测试

getData

？

我查看了Javascript: Mocking Constructor using Sinon但无法提取解决方案。

// test.js
const chai = require('chai');
const sinon = require('sinon');
const should = chai.should();

let Service = require('service');

describe('Service', function() {
  it('getData', function() {
    // throws: TypeError: Attempted to wrap undefined property Service as function
    sinon.stub(Service, 'Service').returns(0);
  });
});

Answer 1

您可以使用

sinon.createStubInstance

创建命名空间或创建存根实例（这不会调用构造函数）。

创建命名空间：

const namespace = {
  Service: require('./service')
};

describe('Service', function() {
  it('getData', function() {
    sinon.stub(namespace, 'Service').returns(0);
    console.log(new namespace.Service()); // Service {}
  });
});

创建存根实例：

let Service = require('./service');

describe('Service', function() {
  it('getData', function() {
    let stub = sinon.createStubInstance(Service);
    console.log(stub); // Service {}
  });
});

Answer 2

您也可以使用proxyquire:

const proxyquire = require('proxyquire');
const sinon = require('sinon');

describe('Service', function() {
    it('getData', function() {
        const internalServiceStub = {
            getEvents: sinon.stub() // mock however you wish
        };
        const InternalServiceStub = sinon.stub().callsFake(() => internalServiceStub);
        const ServiceStub = proxyquire('./service', {
            "./internal-service": InternalServiceStub
        });

        const serviceStub = new ServiceStub();
        // call serviceStub.getData(...) with mocked internalService
    });
});

注意这个解决方案不会调用构造函数。