describe("sum(arr) - sum array of numbers", function() {
    it("should return 3 for [1, 2]", function() {
        expect(sum([1, 2])).to.be.equal(3);
    });
    it("should return 1 for [1]", function() {
        expect(sum([1])).to.be.equal(1);
    });
    it("should return 0 for []", function() {
        expect(sum([])).to.be.equal(0);
    });
    it("should return 3 for [1.5, 2.5, -1]", function() {
        expect(sum([1.5, 2.5, -1])).to.be.equal(3);
    });
    it("should return NaN for invalid data", function() {
        expect(sum("invalid data")).to.be.equal(NaN);
    });
});