Add testing.md doc to describe where specific tests should be added

docs/testing.md

@@ -0,0 +1,26 @@
+# Testing
+
+## Unit tests
+**When**: Pure Go logic, no Kubernetes apiserver or network.
+**Where**: `internal/...`, `pkg/...`  
+**Add files in**: `*_test.go` next to the code.  
+**Run**: `make test`
+
+## Integration tests (envtest)
+**When**: Controller/reconciler behavior against a mocked kubernetes cluster.  
+**Where**: `internal/controller/...`  
+**Framework**: controller-runtime’s `envtest`.  
+**Run**: `make test`
+
+## E2E tests (kind)
+**When**: Full cluster behavior (CRDs, operator image, Connect/SA flows).  
+**Where**: `test/e2e/...`  
+**Framework**: Ginkgo + `pkg/testhelper`.
+
+**Local prep**:
+1. [Install `kind`](https://kind.sigs.k8s.io/docs/user/quick-start/#installing-with-a-package-manager) to spin up local Kubernetes cluster.
+2. `export OP_CONNECT_TOKEN=<token>`
+3. `export OP_SERVICE_ACCOUNT_TOKEN=<token>`
+4. `make test-e2e`
+
+**Run**: `make test-e2e`