core/v1: add unit tests to ensure deprecated protobuf field numbers are not re-used

Signed-off-by: Andrew Sy Kim <kim.andrewsy@gmail.com>

staging/src/k8s.io/api/core/v1/types_test.go

@@ -0,0 +1,41 @@
+/*
+Copyright 2021 The Kubernetes 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.
+*/
+
+package v1
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+)
+
+// Test_ServiceSpecRemovedFieldProtobufNumberReservation tests that the reserved protobuf field numbers
+// for removed fields are not re-used. DO NOT remove this test for any reason, this ensures that tombstoned
+// protobuf field numbers are not accidentally reused by other fields.
+func Test_ServiceSpecRemovedFieldProtobufNumberReservation(t *testing.T) {
+	obj := reflect.ValueOf(ServiceSpec{}).Type()
+	for i := 0; i < obj.NumField(); i++ {
+		f := obj.Field(i)
+
+		protobufNum := strings.Split(f.Tag.Get("protobuf"), ",")[1]
+		if protobufNum == "15" {
+			t.Errorf("protobuf 15 in ServiceSpec is reserved for removed ipFamily field")
+		}
+		if protobufNum == "16" {
+			t.Errorf("protobuf 16 in ServiceSpec is reserved for removed topologyKeys field")
+		}
+	}
+}