One example that has provided me benefit multiple times is a simple Java application that I can run against a String I’m considering as a regular expression token to be used with String.split.

// Note that split() takes a regular expression, so remember to escape special characters if necessary. // there are 12 characters with special meanings: // These special characters are often called ...

The tests directory contains test cases and test programs in Java, Perl, and Python for figuring out what these language's string split function does. Specifically, this is: Java: String.split. Perl: ...