Return not exist error in metadata store

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/metadata/util_test.go

@@ -0,0 +1,35 @@
+/*
+Copyright 2017 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 metadata
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/kubernetes-incubator/cri-containerd/pkg/metadata/store"
+)
+
+func TestIsNotExistError(t *testing.T) {
+	err := store.ErrNotExist
+	assert.True(t, IsNotExistError(err))
+	err = errors.New(store.ErrNotExist.Error())
+	assert.True(t, IsNotExistError(err))
+	err = errors.New("random error")
+	assert.False(t, IsNotExistError(err))
+}