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

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Sep 10, 2025

In this engaging discussion, Will Wilson, Co-founder of Antithesis, reveals how their deterministic hypervisor revolutionizes software testing. He explains the limitations of traditional testing, emphasizing the need for thorough property-based testing to catch unexpected bugs. Listeners learn about simulating entire distributed systems and the challenges of achieving determinism. Fascinatingly, they even discovered glitches in Super Mario Brothers while testing! This conversation is a must for anyone wanting to enhance reliability and confidence in their testing processes.

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INSIGHT

Anticipation Limits Traditional Tests

Test suites rarely catch bugs you didn't anticipate because tests reflect what you already thought about.
Property-style autonomous testing expands coverage by generating scenarios you wouldn't manually write.

ADVICE

Begin With Simple, High-Value Properties

Start with small, high-value properties like "should never crash" and "no uncaught exceptions."
Translate SLAs and documented guarantees into properties to catch systemic failures.

INSIGHT

Loose Specs Make Tests Robust

Writing exact step-by-step integration tests makes them fragile and expensive to maintain.
Property-based rules (e.g., never inside a wall, never crash) stay useful across incidental changes.

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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 the 3am pager alerts? 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.

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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/