Check Knative CustomResourceDefinitions stored version (#2272)

* Check Knative CustomResourceDefinitions stored version

* Use testing.T to log errors

* Address review

test/migrate/checks.go

@@ -0,0 +1,53 @@
+package migrate
+
+/*
+Copyright 2021 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/client/clientset/clientset/typed/apiextensions/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+// ExpectSingleStoredVersion verifies that status.storedVersions on specific CRDs has only one version
+// and the version is listed in spec.Versions with storage: true. It means the CRDs
+// have been migrated and previous/unused API versions can be safely removed from the spec.
+func ExpectSingleStoredVersion(t *testing.T, crdClient apiextensionsv1.CustomResourceDefinitionInterface, crdGroup string) {
+	t.Helper()
+
+	crdList, err := crdClient.List(context.Background(), metav1.ListOptions{})
+	if err != nil {
+		t.Fatal("Unable to fetch crd list:", err)
+	}
+
+	for _, crd := range crdList.Items {
+		if strings.Contains(crd.Name, crdGroup) {
+			if len(crd.Status.StoredVersions) != 1 {
+				t.Errorf("%q does not have a single stored version: %+v", crd.Name, crd)
+			}
+			stored := crd.Status.StoredVersions[0]
+			for _, v := range crd.Spec.Versions {
+				if stored == v.Name && !v.Storage {
+					t.Errorf("%q is invalid: spec.versions.storage must be true for %q or "+
+						"version %q must be removed from status.storageVersions: %+v", crd.Name, v.Name, v.Name, crd)
+				}
+			}
+		}
+	}
+}