I found a template project that uses vitest, which I don't fully understand but I have been able to get working. The key appears to be using @cloudflare/vitest-pool-workers, though I'm unclear if vitest is supposed to be required or not.

https://github.com/cloudflare/workers-sdk/tree/main/packages/create-cloudflare/templates/hello-world/ts https://github.com/cloudflare/workers-sdk/tree/main/packages/vitest-pool-workers