Infrastructure automation testing is hard, but NixOS makes it a breeze. Using NixOS' testing framework, Tumblr developed a comprehensive integration test suite for Jetpants, Tumblr's database automation toolkit designed to manage billions of rows and hundreds of database machines. In this talk we will explore the challenges of testing Jetpants, mimicking complex replication and sharding topologies, and future applications of NixOS at Tumblr.