Edit in JSFiddle

var productBasket = function (products) {
    return {
        total: function () {
            return products.reduce(function (prev, curr) {
                return prev + curr;
            }, 0);
        }
    }
};
 
describe('Product basket', function () {
    describe('#total()', function () {
        it('returns 0 when basket is empty', function () {
            expect(productBasket([]).total()).toEqual(0);
        });
        it('returns price of a single product in the basket', function () {
            expect(productBasket([10]).total()).toEqual(10);
        });
        it('returns price of multiple products in the basket', function () {
            expect(productBasket([10, 20, 30]).total()).toEqual(60);
        });
    })
});