Add a test method?

[TheDougMiester]

Hey, I love your work. The one thing I need your little library to do that it doesn't do already is a quick checkout of the dfplayer at start up. The minirobot version has it (but it's way too bloated for my project-- I have a boatload of suff happening on a nano...)

Df players are really quirky.. if you added a checkout (sd card not inserted, didn't get an rx from it... you know, that stuff) that'd be huge.

Thanks again for putting this on github. You saved me a ton of pain..

-Doug