Testing turns good products into great ones. Every product benefits from it, from the biggest system books to the smallest gazetteers, but too often products go without testing because their creators feel that they don’t have the time or know-how to run tests. It doesn't have to be that way! Pesto's Guide to Testing is a comprehensive guide to TTRPG testing aimed at new creators, but includes plenty of tips and resources for experienced designers as well. Topics ... and much more.
A really useful resource for anyone wanting to make their TTRPG products better. Quick to read, goes directly to the point, and has comprehensive appendices that provide you with everything you need to get the most out of your tests. All of that, and it is free!