When you create a responsive layout you need to test it on multiple resolutions to see if everything works OK and decide or optimize the content that is displayed in each resolution.
Screenqueri.es is a great tool that can help you in your journey of testing such layouts. You just need to define the URL and select the mobile or tablet device. After selecting the URL, the application will load your page and help you see what is going on in each version using the pixel-guided interface.
Also, you are not limited to a pre-defined resolution, having the option to set custom width and height. There is an option to change the orientation also with just a click.