How to spy on a method inside a dependent module using jasmine-node

Question

I am trying to write jasmine tests for a module-(say moduleA) which 'requires' another module-(moduleB).

======> moduleB.js

function moduleBFunction(){
   console.log('function inside moduleB is called');
}

======> moduleA.js

var moduleB = require('./moduleB');
function moduleAfunction(input){
   if(input){
      moduleB.moduleBFunction()
   }

}

I want to write a jasmine test case that tests when i call moduleAfunction, is it calling moduleBfunction or not. I tried to write a test using spyOn(). but i am not sure how can i mock a method inside a dependent module. I did some research and found i might be able to use 'rewire' module for this purpose like below

var moduleB = require('../moduleB');
moduleB.__set__('moduleBfunction', moduleBfunctionSpy);
moduleA.__set__('moduleB', moduleB);
it('should call moduleBfunction', function(){
    moduleA.moduleAfunction()
    expect(moduleB.moduleBfunction()).toHaveBeenCalled()
});

but I feel there should be a simpler way.

Please suggest.

Answer 1

I recommend sinon.js

var sinon = require('sinon')
var moduleA = require('../moduleA')
var moduleB = require('../moduleB')


it('should call moduleBfunction', function() {
  var stub = sinon.stub(moduleB, 'moduleBfunction').returns()
  moduleA.moduleAfunction()
  expect(moduleB.moduleBfunction.calledOnce)
  stub.restore()
})

You can easily fake many different behaviours like:

• stub throws
• stub returns a certain value
• stub yields (mimicking async callback)
• stub works restricted with just for certain input arguments

Don't forget to restore each stub before executing the next test. It's best to use sandboxes and afterEach / beforeEach

describe('tests which require some fakes', function() {
  var sandbox

  beforeEach(function() {
    sandbox = sinon.sandbox.create()
  })

  afterEach(function() {
    sandbox.restore()
  })
})