pkg/invoke: refactor plugin exec and backfill unit tests

pkg/invoke/fakes/version_decoder.go

@@ -0,0 +1,34 @@
+// Copyright 2016 CNI 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 fakes
+
+import "github.com/containernetworking/cni/pkg/version"
+
+type VersionDecoder struct {
+	DecodeCall struct {
+		Received struct {
+			JSONBytes []byte
+		}
+		Returns struct {
+			PluginInfo version.PluginInfo
+			Error      error
+		}
+	}
+}
+
+func (e *VersionDecoder) Decode(jsonData []byte) (version.PluginInfo, error) {
+	e.DecodeCall.Received.JSONBytes = jsonData
+	return e.DecodeCall.Returns.PluginInfo, e.DecodeCall.Returns.Error
+}