From Unit Tests to Whole Universe Tests (with Will Wilson)

How confident are you when your test suite goes green? If you're honest, probably not 100% confident - because most bugs come from scenarios we never thought to test. Traditional testing only catches the problems we anticipate, but what about the bugs you never saw coming? Those come from the unexpected interactions, timing issues, and edge cases we never imagined. In this episode, Will Wilson from Antithesis takes us deep into the world of autonomous testing. They've built a deterministic hypervisor that can simulate entire distributed systems - complete with fake AWS services - and intelligently explore millions of possible states to find bugs before production. Think property-based testing, but for your entire infrastructure stack. The approach is so thorough they've even used it to find glitches in Super Mario Brothers (seriously). We explore how deterministic simulation works at the hypervisor level, why traditional integration tests are fundamentally limited, and how you can write maintainable tests that actually find the bugs that matter. If you've ever wished you could test "what happens when everything that can go wrong does go wrong," this conversation shows you how that's finally becoming possible. --- Support Developer Voices on Patreon: https://patreon.com/DeveloperVoices Support Developer Voices on YouTube: https://www.youtube.com/@DeveloperVoices/join Antithesis: https://antithesis.com/ Antithesis testing with Super Mario: https://antithesis.com/blog/sdtalk/ ...and with Metroid: https://antithesis.com/blog/2025/metroid/ MongoDB: https://www.mongodb.com/ etcd (Linux Foundation): https://etcd.io/ Facebook Hermit: https://github.com/facebookexperimental/hermit RR (Record-Replay Debugger): https://rr-project.org/ T-SAN (Thread Sanitizer): https://clang.llvm.org/docs/ThreadSanitizer.html Toby Bell's Strange Loop Talk on JPL Testing: https://www.youtube.com/results?search_query=toby+bell+strange+loop+jpl Andy Weir - Project Hail Mary: https://www.goodreads.com/book/show/54493401-project-hail-mary Andy Weir - The Martian: https://www.goodreads.com/book/show/18007564-the-martian Antithesis Blog (Nintendo Games Testing): https://antithesis.com/blog/ Kris on Bluesky: https://bsky.app/profile/krisajenkins.bsky.social Kris on Mastodon: http://mastodon.social/@krisajenkins Kris on LinkedIn: https://www.linkedin.com/in/krisjenkins/ --- 0:00 Intro 3:12 The Problem with Traditional Testing 6:28 Property Testing & Antithesis Overview 9:57 Specifying Tests for Distributed Systems 15:00 Nintendo Games & Practical Examples 20:00 The Deterministic Hypervisor 28:45 Nintendo Emulation & Technical Details 30:00 Deterministic Replay & System Isolation 40:00 Advanced Techniques: Forking from Seeds 50:00 Coverage-Guided Testing & Smart Exploration 1:00:00 Real-World Applications & Client Stories 1:05:15 Deep Dive: Nintendo Games & Emulation 1:10:25 NASA, Space Systems & Future Applications 1:11:08 Outro