Adding my own instructions for agents (#5147)

NO_CHANGELOG=true

## Changes
<!-- Summary of your changes that are easy to understand -->

## Tests
<!--
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->

- [ ] `make test` run locally
- [ ] relevant change in `docs/` folder
- [ ] covered with integration tests in `internal/acceptance`
- [ ] using Go SDK
- [ ] using TF Plugin Framework
- [ ] has entry in `NEXT_CHANGELOG.md` file

Author: alexott

AGENTS.md

@@ -120,10 +120,16 @@ Some Unity Catalog resources (e.g., storage credentials, external locations) wor
 
 ### Code Organization
 - Files should not exceed 600 lines
+- don't make changes in files that have `DO NOT EDIT` in the first line
 - Functions should fit on a 13" screen (max 40 lines, except tests)
 - No unnecessary package exports (avoid public structs/types unless needed outside package)
 - Use `qa.EnvironmentTemplate()` instead of complex `fmt.Sprintf` with >4 placeholders
 
+### Writing unit tests for resources and data sources
+
+For unit tests use the `MockWorkspaceClientFunc` from Databricks Go SDK instead of `HTTPFixture`.
+Use `ApplyAndExpectData` where it's possible.
+
 ### Import Conventions
 Order imports as: Go standard library, vendor packages, current provider packages.
 Within each section, maintain alphabetical order.
@@ -145,4 +151,4 @@ All user-facing changes must be documented in `NEXT_CHANGELOG.md` with format:
 ### Migration Verification
 When migrating resources to Plugin Framework, always run `make diff-schema` to ensure no breaking changes to the Terraform schema.
 
-- Always run make fmt before making any commit.
+- Always run `make fmt lint ws` before making any commit.