My responsive testing tool is located at: https://github.com/tomhodgins/speedtest You can use your keyboard keys 1-0 to test a variety of widths quickly, or use the buttons on mobile to test widths your phone or tablet can't physically emulate
You can also check out my CodePen profile, here's my collection of 'Front-end snippets', but I've got plenty more on there you can feel free to use or expand on: http://codepen.io/collection/nNqyvZ/