Intergation testing with `vitest-pool-workers` and fetchMock

[timkelty]

I was trying to implement some integration/e2e tests to test ESI parsing using vitest-pool-workers, which seems to be Cloudflare's latest and greatest offering for testing workers.

I discovered it gets tricky pretty quickly, as you want to mock the responses from origin, but still let cloudflare-esi do it's thing.

Anyway, just curious if you've dabbled with it at all, or if you think it'd be worth sharing where I'm at with my implementation.