Testing Strategy

[aviramha]

I think we're all a bit hateful towards the CI, and for good reasons. I believe that the way to improve it is by having a more consistent testing strategy, and the implementation of it.

I propose of the following strategy (priority included):

1. Unit tests - Rust modules should have UT to test it's logic. I think this is less of a problem due to the compiler nature to save us from ourselves, so this is least prioritized but should be in new code.
2. Integration tests
   a. Add mirrord-layer tests that doesn't need k8s or real agent. Setup a mock agent to communicate against and verify the flow with different operating system, programming languages and frameworks - this is the most important in my opinion as it's faster to run, most value in terms of integration (checking that hooks work) and saving us time.
   b. Add mirrord-agent tests - we already have some integration tests there that create a "fake" client that interacts with the agent, we should have it more robust and cover most agent features.
3. E2E tests - Should be the bare minimum, sanity microservice that runs in different docker runtimes, and ephemeral containers/job. Focus is on K8S integration. - This is to be done after 2 so then we actually get the benefits of the change. (by reducing tests here)

tl;dr -> implement IT, reduce E2E, add UT.