http://norvig.com/spell-correct.html
https://news.ycombinator.com/item?id=16918757
blog-post-how-to-write-a-spell-corrector#two-separate-tests1"From that I extracted two test sets of corrections. The first is for development, meaning I get to look at it while I'm developing the program. The second is a final test set, meaning I'm not allowed to look at it, nor change my program after evaluating on it. This practice of having two sets is good hygiene; it keeps me from fooling myself into thinking I'm doing better than I am by tuning the program to one specific set of tests." blog-post-how-to-write-a-spell-corrector#two-separate-tests1