如何使用sinon模拟用此关键字定义的函数？

Question

我有一个功能foo

var foo = function(){
    this.doRandomStuff = function(callback){
      //do Something
      callback(false);
    }
}
var bar = function(){
    var fooInstance = new foo();
    fooInstance.doRandomStuff(function(val){
      //do Something with val
    })
}

我想为bar功能编写测试，为此我正在使用mocha和sinon。

describe("Foo Test",function(){
      it("testing foo",function(done){
         var instance = new foo();

         sinon.stub(instance,'doRandomStuff').callsArgWith(0,true); // This Doesn't work
         sinon.stub(foo,'doRandomStuff').callsArgWith(0,true); // This also Doesn't work

         bar();
         done();
      })
});

我得到以下异常：

TypeError：无法存根不存在的自己的属性doRandomStuff

Answer 1

使其更易于测试的替代方法是模块方法，如下所示：

foo.js

function doRandomStuff(callback) {
  callback(false);
}

module.exports = {
  doRandomStuff
}

bar.js

const foo = require('./foo');

module.exports = function() {
  foo.doRandomStuff(function(val) {
    console.log('test val', val); // for testing purpose
  })
}

test.js

const sinon = require('sinon');
const foo = require('./foo');
const bar = require('./bar');

describe('Foo Test', function() {
  it("testing foo",function(done){
    sinon.stub(foo, 'doRandomStuff').callsArgWith(0,true); 

    bar(); // output: "test val true"
    done();
 });
});