test(webhook): add nodeName clear test + compile-time interface assertions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: syscod3

internal/webhook/v1alpha1/impvm_webhook.go

@@ -28,6 +28,11 @@ import (
 // ImpVMWebhook implements defaulting and validation for ImpVM.
 type ImpVMWebhook struct{}
 
+var (
+	_ admission.Defaulter[*impdevv1alpha1.ImpVM] = &ImpVMWebhook{}
+	_ admission.Validator[*impdevv1alpha1.ImpVM] = &ImpVMWebhook{}
+)
+
 // Default implements admission.Defaulter[*impdevv1alpha1.ImpVM].
 func (w *ImpVMWebhook) Default(_ context.Context, vm *impdevv1alpha1.ImpVM) error {
 	if vm.Spec.Lifecycle == "" {

internal/webhook/v1alpha1/impvm_webhook_test.go

@@ -165,6 +165,20 @@ func TestImpVMWebhook_ValidateUpdate_NodeNameUnchanged(t *testing.T) {
 	}
 }
 
+func TestImpVMWebhook_ValidateUpdate_NodeNameCannotBeCleared(t *testing.T) {
+	wh := &ImpVMWebhook{}
+	old := newVM("my-template", "", "")
+	old.Spec.NodeName = "node-1"
+
+	updated := newVM("my-template", "", "")
+	updated.Spec.NodeName = "" // attempt to clear — should be rejected
+
+	_, err := wh.ValidateUpdate(context.Background(), old, updated)
+	if err == nil {
+		t.Fatal("expected error when clearing a set nodeName")
+	}
+}
+
 // --- ValidateDelete tests --------------------------------------------------
 
 func TestImpVMWebhook_ValidateDelete(t *testing.T) {