add validation transformer

plugin/someteam.example.com/v1/validator/Validator

@@ -0,0 +1,35 @@
+#!/bin/bash
+
+
+# Validator transformer plugin by kubeval
+# https://github.com/instrumenta/kubeval
+#
+# Assumes that kubeval is available from $PATH
+#
+# Reads Kubernetes resources from stdin
+# Validates them and output in the stdout
+#
+# Example execution:
+# cat <raw K8s yaml> | ./plugin/someteam.example.com/v1/Validator
+
+if ! [ -x "$(command -v kubeval)" ]; then
+  echo "Error: kubeval is not installed."
+  exit 1
+fi
+
+temp_file=$(mktemp)
+output_file=$(mktemp)
+cat - > $temp_file
+
+kubeval $temp_file > $output_file
+
+if [ $? -eq 0 ]; then
+    cat $temp_file
+    rm $temp_file $output_file
+    exit 0
+fi
+
+cat $output_file
+rm $temp_file $output_file
+exit 1
+

plugin/someteam.example.com/v1/validator/validator_test.go

@@ -0,0 +1,79 @@
+// +build notravis
+
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package main_test
+
+import (
+	"strings"
+	"testing"
+
+	"sigs.k8s.io/kustomize/pkg/kusttest"
+	"sigs.k8s.io/kustomize/plugin"
+)
+
+func TestValidatorHappy(t *testing.T) {
+	tc := plugin.NewEnvForTest(t).Set()
+	defer tc.Reset()
+
+	tc.BuildExecPlugin("someteam.example.com", "v1", "Validator")
+	th := kusttest_test.NewKustTestPluginHarness(t, "/app")
+
+	rm := th.LoadAndRunTransformer(`
+apiVersion: someteam.example.com/v1
+kind: Validator
+metadata:
+  name: notImportantHere
+`,
+		`apiVersion: v1
+kind: ConfigMap
+metadata:
+  annotations:
+    foo: bar
+  name: some-cm
+data:
+  foo: bar
+`)
+
+	th.AssertActualEqualsExpected(rm, `
+apiVersion: v1
+data:
+  foo: bar
+kind: ConfigMap
+metadata:
+  annotations:
+    foo: bar
+  name: some-cm
+`)
+}
+
+func TestValidatorUnHappy(t *testing.T) {
+	tc := plugin.NewEnvForTest(t).Set()
+	defer tc.Reset()
+
+	tc.BuildExecPlugin("someteam.example.com", "v1", "Validator")
+	th := kusttest_test.NewKustTestPluginHarness(t, "/app")
+
+	err := th.ErrorFromLoadAndRunTransformer(`
+apiVersion: someteam.example.com/v1
+kind: Validator
+metadata:
+  name: notImportantHere
+`,
+		`apiVersion: v1
+kind: ConfigMap
+metadata:
+  annotations: {}
+  name: some-cm
+data:
+- foo: bar
+`)
+	if err == nil {
+		t.Fatalf("expected an error")
+	}
+	if !strings.Contains(err.Error(),
+		"data: Invalid type. Expected: object, given: array") {
+		t.Fatalf("incorrect error %v", err)
+	}
+}