Edit in JSFiddle

describe('toBeNull', function() {
    it('passes if subject is null', function() {
        expect(null).toBeNull();
    });

    it('fails if subject is undefined', function() {
        expect(undefined).not.toBeNull();
    });

    it('fails if subject is no null', function() {
        expect({}).not.toBeNull();
    });
});

execJasmine();