It is true. The only people resizing their browser windows are the web designers.
Me for instance: I do not proudly possess an iPad or any other tablet. I do not have an iPhone, nor a BlackBerry or any other Internet connected small device. (I do own an ancient Nokia though, from Before Time Was Time!)
So I have to resize my browser windows to test all media query break points. What else?
You could use this testpage with some pre-defined iframes: Matt Kersley’s tool. Whereupon @lensco tweaked that page (Simple responsive design test page) and, at last, points out this Responsive Design Test Bookmarklet. All very convenient for a quick glance.
There are several online emulators as well, like iPad Peek.
And ultimately Opera offers a smooth and stylish desktop Mobile Emulator. As they say ‘Do your mobile development straight from your desktop, and pair it with Opera Dragonfly for advanced debugging’.
The emulator comes with a launcher where infinite instances can be defined.
For this I added a new category: Handy!