Sinon.spy is not called in a method

The code I'm testing is pretty simple: it calls a method when a condition is checked. If not, it calls another method contained in the first one as an attribute.

app.js:

function test (fn, isActivated) {
  if (isActivated) {
    return fn('foo')
  }

  return fn.subFn('bar')
}

var fn = function (p) { return p }
fn.subFn = function (p) { return 'sub-' + p }

var resFn = test(fn, true)
var resSubFn = test(fn, false)

document.write(resFn) // shows 'foo' as expected
document.write(resSubFn) // shows 'bar' as expected
      

        
        
        
      

    

I installed spy for each method, but spy for method fn

does not work while spy for contained method is running subFn

. See below:

app.test.js:

'use strict'

const chai = require('chai')
const sinon = require('sinon')
const trigger = require('../app').trigger

chai.should()

describe('test app', function () {
    before(function () {
      this.fn = function () {}
      this.fn.subFn = function () {}
      this.subFnSpy = sinon.spy(this.fn, 'subFn')
      this.fnSpy = sinon.spy(this.fn)
    })

    describe('isActivated is true', function () {
      before(function () {
        trigger(this.fn, true)
      })

      it('should invoke fn', function () {
        this.fnSpy.callCount.should.equal(1) // return false because callCount = 0
      })
    })

    describe('isActivated is false', function () {
      before(function () {
        trigger(this.fn, false)
      })

      it('should invoke subFn', function () {
        this.subFnSpy.callCount.should.equal(1) // return false because callCount = 0
      })
    })
  })

      

        
        
        
      

    

Having inflicted something wrong with the spy on the function fn

, I tried with two separate methods. Both spies do not work in this case:

app.js:

exports.trigger = function (fn, subFn, isActivated) {
  if (isActivated) {
    return fn('fn')
  }

  return subFn('bar')
}

      

        
        
        
      

    

app.test.js

'use strict'

const chai = require('chai')
const sinon = require('sinon')
const trigger = require('../app').trigger

chai.should()

describe('test app', function () {
    before(function () {
      this.fn = function () {}
      this.subFn = function () {}
      this.fnSpy = sinon.spy(this.fn)
      this.subFnSpy = sinon.spy(this.subFn)
    })

    beforeEach(function () {
      this.fnSpy.reset()
      this.subFnSpy.reset()
    })

    describe('isActivated is true', function () {
      before(function () {
        trigger(this.fn, this.subFn, true)
      })

      it('should invoke fn if isActivated is true', function () {
        this.fnSpy.callCount.should.equal(1) // return false
      })
    })

    describe('isActivated is false', function () {
      before(function () {
        trigger(this.fn, this.subFn, false)
      })

      it('should invoke subFn if isActivated is true', function () {
        this.subFnSpy.callCount.should.equal(1) // return false
      })
    })
  })

      

        
        
        
      

    

Any suggestion on what I am doing wrong?