Add sandbox store helpers

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

sandbox/store_test.go

@@ -0,0 +1,40 @@
+/*
+   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 sandbox
+
+import (
+	"testing"
+
+	"github.com/containerd/typeurl"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAddExtension(t *testing.T) {
+	sb := Sandbox{ID: "1"}
+
+	type test struct{ Name string }
+
+	typeurl.Register(&test{})
+
+	var in = test{Name: "test"}
+	assert.NoError(t, sb.AddExtension("test", &in))
+
+	var out test
+	err := sb.GetExtension("test", &out)
+	assert.NoError(t, err)
+	assert.Equal(t, "test", out.Name)
+}