Sinon Spy is not called if the spied method is called indirectly

Question

Problem

In our codebase we have a problem with sinon which can be reproduced with the code snipped below. The thing is that it seems to be that indirect called spies return force false, the console.log clearly states that the method is called but the spy.called remains false.

Code

The following CDN's can be used for the html:

//cdnjs.cloudflare.com/ajax/libs/sinon.js/1.7.3/sinon-min.js
//cdnjs.cloudflare.com/ajax/libs/require.js/2.1.14/require.min.js

main.js

require(['myModule'], function(module) {

    //using sinon
    var methodCallerSpy = sinon.spy(module, 'methodCaller')
    console.log(methodCallerSpy); // methodCaller
    module.methodCaller();
    console.log(methodCallerSpy.called); //true


    var methodSpy = sinon.spy(module, 'method');
    console.log(methodSpy); //method
    module.methodCaller();
    console.log(methodSpy.called); // false
    module.method();
    console.log(methodSpy.called); // true

});

And the module

define(function() {
    const method = () => console.log('method called by methodCaller');

    const methodCaller = () => method();

    return{
        method,
        methodCaller
    }
});

Answer 1

The problem is that myModule has two private functions called method() and methodCaller() as well as two methods it exposes with the same names.

Sinon is capable on spying on the exposed methods, but not the internal functions.

When you call module.method() your invoking the exposed method, so Sinon is able to detect the call. However, when you call method.methodCaller(), methodCaller() calls the method() private function directly, and therefore the call is not detected by Sinon.

If you change your methodCaller() function to:

methodCaller = function(){
    this.method();
}

... then Sinon should be able to capture the "indirect" call to method() when calling methodCaller().