/testfor command not working with player names and modifiers

I tried to create a locked door in Vanilla MC with command blocks using my username, the /testfor command, and the modifier

{r=<some number>}. (yes i used square brackets, but they don't show here.) Even when I was within the testing radius, the command always failed. Obviously, the intended result was a piston door that could only be operated by me (yes I was using a comparator). I know that I wired it right because if i take out {r=<some number>}

then it works. Help?