davekt

https://typing.io/lessons let you type through code, which exercises the right pinky more than prose. The site also requires backspacing to correct typos. This adds realistic overhead not normally captured in wpm measurements.

For a production ready alternative, take a look at http://creditcardjs.com, which was posted on HN a while back. The web site points out common mistakes when implementing credit card forms and delves into the motivation behind every design decision.