Fix tests

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

protobuf/compare.go

@@ -0,0 +1,41 @@
+/*
+   Copyright The containerd 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 protobuf
+
+import (
+	"github.com/google/go-cmp/cmp"
+	"google.golang.org/protobuf/proto"
+)
+
+var Compare = cmp.FilterValues(
+	func(x, y interface{}) bool {
+		_, xok := x.(proto.Message)
+		_, yok := y.(proto.Message)
+		return xok && yok
+	},
+	cmp.Comparer(func(x, y interface{}) bool {
+		vx, ok := x.(proto.Message)
+		if !ok {
+			return false
+		}
+		vy, ok := y.(proto.Message)
+		if !ok {
+			return false
+		}
+		return proto.Equal(vx, vy)
+	}),
+)