# Alfonso Subiotto Marqués - (Mostly) Deterministic Simulation Testing in Go (Highlights) %20Deterministic%20Simulation%20Testing%20in%20Go&authors=Alfonso%20Subiotto%20Marqu%C3%A9s&tags=Testing,Go,FrostDB,Golang,Debugging,Databases,Deterministic%20Simulation%20Testing) ## Metadata **Review**:: [readwise.io](https://readwise.io/bookreview/61299488) **Source**:: #from/readwise #from/reader **Zettel**:: #zettel/fleeting **Status**:: #x **Authors**:: [[Alfonso Subiotto Marqués]] **Full Title**:: (Mostly) Deterministic Simulation Testing in Go **Category**:: #articles #readwise/articles **Category Icon**:: 📰 **Document Tags**:: #via/ddia **URL**:: [www.polarsignals.com](https://www.polarsignals.com/blog/posts/2024/05/28/mostly-dst-in-go) **Host**:: [[www.polarsignals.com]] **Highlighted**:: [[2026-06-13]] **Created**:: [[2026-06-20]] ## Highlights - At this point a bit of pattern-matching occurred and we recalled that it was possible to compile Go programs to WASM and run them on a [WASM runtime](https://go.dev/blog/wasi) that implements the WebAssembly syscall interface (wasip1). ([View Highlight](https://read.readwise.io/read/01kv1fnpzjamk7tkzdtx44m489)) ^1025008288 - Thankfully, all random choices in the runtime use a global random number generator seeded at startup, including the rand package exposed to the Go application. This seed is [read using the OS-specific `readRandom` function](https://github.com/golang/go/blob/35ef4a9f330fdff870ff637558ec2fd03a93fd9c/src/runtime/rand.go#L51). There is no way to provide this seed at startup, so we ended up modifying the Go runtime to read the seed via an environment variable. ([View Highlight](https://read.readwise.io/read/01kv1fqxky5szk3dcc3g7zd2c4)) ^1025010162 - The key idea is that time starts at a fixed timestamp and only advances when all goroutines are blocked. ([View Highlight](https://read.readwise.io/read/01kv1fsry4hyd7gqnsrcmeyqbm)) ^1025011615