cd_warehouse_test.js

const assert = require('assert');

function Warehouse(catalogue) {
    this.catalogue = catalogue;

    this.getCd = function (artist, title) {
        return this.catalogue.find((cd) => cd.artist == artist && cd.title == title);
    };

    this.buyCd = function (artist, title, catalogue) {
        const cd = this.getCd(artist, title, catalogue);
        cd.buy();
        return this.catalogue;
    };
}

function CD(artist, title, stock) {

    this.artist = artist;
    this.title = title;
    this.stock = stock;

    this.getStock = function () {
        return this.stock;
    };

    this.buy = function () {
        this.stock -= 1;
    };

    this.matches = function (artist, title) {
        return this.artist == artist && this.title == title;
    };
}
describe('CD Warehouse', () => {
    it('reduces stock count by 1 of bought CD', () => {

        const cd = new CD('Peter Gabriel', 'So', 1);

        let catalogue = [
            cd
        ];

        const warehouse = new Warehouse(catalogue);
        warehouse.buyCd('Peter Gabriel', 'So');
        assert.equal(cd.getStock(), 0);
    });
});