The Minitest Cookbook is full of techniques for writing clear, effective, and maintainable tests with Minitest. Even if you're more into RSpec right now, this one might convert you.
This book provides an excellent overview of the guts of how Minitest works. You will learn how to design efficient, maintainable tests with a framework that comes in Ruby's default installation. After reading this, you may feel that a lot of the points in ye ole RSpec vs Minitest debate are just due to a lack of understanding. Minitest is extremely versatile, and this book shows you how to solve both every-day and niche problems. You will also learn how to customize it with your plugins. In addition to covering Minitest thoroughly, you'll learn good testing practices to help you avoid maintenance nightmares.