I posted my article Build Your Own Regex Engine on Reddit the other day, and one of the commenters claimed that the implementation should be trivial to break. Since I had already tested my program against a customized suite of tests, the remark got me thinking about how I could further increase my confidence in the correctness of my program. One extremely low cost however effective strategy for identifying faults in software is known as fuzzing.

I stumbled upon an article the other day where Rob Pike implements a rudimentary regular expression engine in c. I converted his code to Javascript and added test specs so that someone can self-guide themselves through the creation of the regex engine. The specs and solution can be found in this GitHub repository. This blog post walks through my solution.