Sinon spy on function expression

Question

is it possible to make sinon spy on function expressions? Look this code for example.

function one() { return 1; }
function two() { return 2; }
function three() { return 3; }

function myMethod() {
  var n1 = one();
  var n2 = two();
  var n3 = three();
  return n1 + n2 + n3;
}


QUnit.module('My test');

QUnit.test('testing functions', (assert) => {
  assert.expect(3);
  
  const spyOne = sinon.spy(one);
  const spyTwo = sinon.spy(two);
  const spyThree = sinon.spy(three);
 myMethod();

  assert.ok(spyOne.called, "called one");
  assert.ok(spyTwo.called, "called two");
  assert.ok(spyThree.called, "called three");
  
  sinon.restore();
});

Even though I call myMethod() and I have spies on one - two - three I still get false on one.called (same for two and three)

What am I missing here?

Thanks!

Possible duplicate of [Verifying function call and inspecting arguments using sinon spies](https://stackoverflow.com/questions/29800733/verifying-function-call-and-inspecting-arguments-using-sinon-spies) — try-catch-finally, Jul 05 '17 at 05:29

robertklep · Accepted Answer · 2016-05-08T08:01:18.153

Calling sinon.spy(fn) doesn't change fn, it merely creates a new function (the spy) that will call fn.

For you to be able to test one, two, three, you need to replace those functions (or rather, their references) with spies, and restore them afterwards:

// keep references to the original functions
var _one   = one;
var _two   = two;
var _three = three;

// replace the original functions with spies
one   = sinon.spy(one);
two   = sinon.spy(two);
three = sinon.spy(three);

// call our method
myMethod();

// test
assert.ok(one.called,   "called one");
assert.ok(two.called,   "called two");
assert.ok(three.called, "called three");

// restore the original functions
one   = _one;
two   = _two;
three = _three;

It's not ideal though, and if possible I would probably group all the functions into an object. That would also enable Sinon to restore the originals itself.

This only works if you have the function definitions and test in the same file, which is rarely the case. — Govind Rai, Jan 29 '21 at 18:10
@GovindRai correct, but I'm not offering a solution for that particular issue. I'm just explaining why the original code in the question doesn't work as expected and how to work around that. — robertklep, Jan 30 '21 at 14:59

Sinon spy on function expression

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