Jasmine Testing - How to test for a class being applied?

I am currently creating my first JS project and am trying Jasmine unit testing for the first time.

In my code, I want to test the function in one of my classes which applies a css class to a button element. However I am having difficulty getting the Jasmine test to pass and I am not sure why.

The test fails due to the test not seeing the class '.btn-active' in the targeted button, which is telling me that the function is not running, however I am unsure as to how to achieve this.

JS Class:

class ModeSelection {
        constructor() {
                this.easyBtn = $('#easy-mode');
                this.mediumBtn = $('#medium-mode');
                this.hardBtn = $('#hard-mode');
        }
        //applies the active class depending upon the button selected
        easyMode() {
                this.easyBtn.on('click', () => {
                        this.easyBtn.addClass('btn-active');
                        this.mediumBtn.removeClass('btn-active');
                        this.hardBtn.removeClass('btn-active');

                        $('.card-med').addClass('remove');
                        $('.card-hard').addClass('remove');
                });
        }

Please note, I have set a fixture before each test which contains the html button that I am looking to apply the class too.

Jasmine Test:

 describe('Check easy mode functions', function() {
        beforeEach(function() {
            this.mode = new ModeSelection();

        });

      it('btn-active to be applied when easy function activated', function() {

            var spy = spyOn(this.mode, 'easyMode').and.callThrough();


            expect($('#easy-mode')).toHaveClass('btn-active')
        });

 });

Apologies if this is fairly basic, however I am quite new to Jasmine and was just seeking the best way to get this test to work.

Thank

Sam