express javascript node.js supertest testing

supertest test express middleware

found the following hint on how to test middleware in express:
I was wondering why my tests were always passing. Until I noticed that when i copied the test from express they behaved the same. I tried screwing them up but they keep passing:

What am I missing here?

it('should return true when X-Requested-With is xmlhttprequest', function(done){
var app = express();
app.use(function(req, res){; //set to false, to fail the test but it still passes
.set('X-Requested-With', 'xmlhttprequest')