Summary

• Add the ability to easily mock a tRPC backend for usage in things like storybook, jest, etc

Background

There are many use cases for mocking beyond "writing to a database.

Two that immediately come to mind for our use case:

1. Using a mock API for stories (Storybook, Ladle). For this use case, even if we could use a real endpoint, it wouldn't be a good idea, as one generally wants to control the data and not have some gibberish mock data created by test users.
2. Endpoints that go beyond database calls. We have a use case that requires a tight integration with many AWS services, including ones that would bill you a lot, if you were just creating these resources for testing. In this case also running a live API isn't even feasible locally. And deploying an actual API can take many minutes. So you can't even tear it down for each test.

I agree on integration > mocking premise in general. But there are some cases that are just not feasible without having mocks.

Originally posted by @moltar in https://github.com/trpc/trpc/discussions/1879#discussioncomment-3395657

Todos

• Create spec/RFC on how mocking should look like
• Implement said mocking

_T-75