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.

lipp · Accepted Answer · 2016-05-05T12:01:48.630

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()
  })
})

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

1 Answers1