I was asked to complete a screening test on CoderPad earlier this year and got rejected because, from what I could tell, my edits didn't sync with their backend for some reason. Of course I couldn't prove it so I can't blame the company. It sucks because I came up with what I thought was a pretty good solution to the problem. Make a copy and attach it in a notification email to your interviewer!

Anyway, just one more reason to be weary of these types of tools.