Recently, we've been writing extensive unit test coverage of our controllers using fake.Client but a few of our controllers use client.Apply, which is not supported by fake.Client.

We can't migrate these controllers from client.Apply to client.Merge because with upgrades, any CRs managed by the previous version will have owned fields and the API server will reject the request (my understanding, is this true?) based on the SSA docs it seems the server would only reject requests based on ownership when using SSA, so using update would work.

Envtest takes ~5-15s to set up for each test case, meaning a test suite which would take 0.05s with fake.Client, takes 5 minutes with envtest. In many cases, we can isolate tests to namespaces and reuse the same client, but not always. We prefer our unit tests to be as isolated as possible.

Would it be possible to support server-side apply / client.Apply / SSA in the fake client?