How to mock variable with Sinon/Mocha in node.js

Question

This is my code: start_end.js

var glb_obj, test={};
var timer = 10;

test.start_pool = function(cb) {
   timer--;
   if(timer < 1) {
     glb_obj = {"close": true}; // setting object
     cb(null, "hello world");    
   } else {
     start_pool(cb);
   }
}

test.end_pool = function(){
  if(glb_obj && glb_obj.close) {
    console.log("closed");
  }
}

module.exports = test;

Testcase:

var sinon = require('sinon');
var start_end = require('./start_end');

describe("start_end", function(){ 
   before(function () {
      cb_spy = sinon.spy();
   });

   afterEach(function () {
    cb_spy.reset();
   });

  it("start_pool()", function(done){
     // how to make timer variable < 1, so that if(timer < 1) will meet
     start_end.start_pool(cb_spy);
     sinon.assert.calledWith(cb_spy, null, "hello world");  

  });
});

how to change the variable timer and glb_obj within the functions using sinon?

Solution 1

This is not possible using Sinon as of v4.1.2.

Sinon focuses on testing behaviour through stubbing and mocking - rather than changing internal state.

---

If you want to change the values of the private variables, look into using something like rewire:

https://github.com/jhnns/rewire

Solution 2

If someone wants to still stub with Sinon, we can stub the getters method and mock get method of the object tested, and works fine for me

sinon.stub(myObj, 'propertyName').get(() => 'mockedValue');

Comments

[SomeDutchGuy]

This will not work for variables declared inside a function. I know it is not related to this case but decided to say so in case others come here with a similar question.

[user3019802]

Did you ever find a solution to this issue? I'm currently trying to mock a variable inside a function. This variable awaits on a function that generates a token from an API call. I can't seem to populate the variable with a mocked token.

[Irfan Raza]

Great. This worked.