Don’t confuse design testing with device testing — Stuff
Andy makes a good point here, point out the difference between device testing and design testing:
When I’m designing, it’s incredibly important for me to quickly gain an affinity with how my design feels when I hold it in my hands.
These are not device testing issues, they are design questions and there’s a huge difference between how an interface feels to use on a smartphone size display and whether the HTML, CSS and Javascript actually works on any particular make or model.