We have quite a number of projects with responsive layout implemented on. It is necessary to check that behavior on various type of devices and screen sizes. There is a Firefox plugin named Web Developer Toolbar which can help you on this. If you dont have this plugin already, go for it right now.
Now, about the responsive layout testing, Go to:
Resize > View Responsive Layouts
A new page will be opened with all types and sized viewports where you can test and check how your page is behaving. Enjoy!