Deterministic simulation testing (DST) is a technique for fully reproducible, randomized system testing. Pioneered by FoundationDB a decade ago, DST is gaining momentum in the industry, with companies such as TigerBeetle and Dropbox building distributed systems with it. In this talk, we'll look at what DST is, how it compares to other techniques such as chaos testing, property-based testing, and more, and what it means to build systems in deterministic ways.