improve error message in json patch transformer

pkg/patch/transformer/patchjson6902json_test.go

@@ -18,9 +18,9 @@ package transformer
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 
-	"github.com/evanphx/json-patch"
 	"sigs.k8s.io/kustomize/k8sdeps/kunstruct"
 	"sigs.k8s.io/kustomize/pkg/gvk"
 	"sigs.k8s.io/kustomize/pkg/resid"
@@ -67,10 +67,7 @@ func TestJsonPatchJSONTransformer_Transform(t *testing.T) {
         {"op": "add", "path": "/spec/replica", "value": "3"},
         {"op": "add", "path": "/spec/template/spec/containers/0/command", "value": ["arg1", "arg2", "arg3"]}
 ]`)
-	patch, err := jsonpatch.DecodePatch(operations)
-	if err != nil {
-		t.Fatalf("unexpected error : %v", err)
-	}
+
 	expected := resmap.ResMap{
 		id: rf.FromMap(
 			map[string]interface{}{
@@ -104,7 +101,7 @@ func TestJsonPatchJSONTransformer_Transform(t *testing.T) {
 				},
 			}),
 	}
-	jpt, err := newPatchJson6902JSONTransformer(id, patch)
+	jpt, err := newPatchJson6902JSONTransformer(id, operations)
 	if err != nil {
 		t.Fatalf("unexpected error : %v", err)
 	}
@@ -117,3 +114,52 @@ func TestJsonPatchJSONTransformer_Transform(t *testing.T) {
 		t.Fatalf("actual doesn't match expected: %v", err)
 	}
 }
+
+func TestJsonPatchJSONTransformer_UnHappyTransform(t *testing.T) {
+	rf := resource.NewFactory(
+		kunstruct.NewKunstructuredFactoryImpl())
+	id := resid.NewResId(deploy, "deploy1")
+	base := resmap.ResMap{
+		id: rf.FromMap(
+			map[string]interface{}{
+				"apiVersion": "apps/v1",
+				"kind":       "Deployment",
+				"metadata": map[string]interface{}{
+					"name": "deploy1",
+				},
+				"spec": map[string]interface{}{
+					"template": map[string]interface{}{
+						"metadata": map[string]interface{}{
+							"labels": map[string]interface{}{
+								"old-label": "old-value",
+							},
+						},
+						"spec": map[string]interface{}{
+							"containers": []interface{}{
+								map[string]interface{}{
+									"name":  "nginx",
+									"image": "nginx",
+								},
+							},
+						},
+					},
+				},
+			}),
+	}
+
+	operations := []byte(`[
+        {"op": "add", "path": "/spec/template/spec/containers/0/command/", "value": ["arg1", "arg2", "arg3"]}
+]`)
+
+	jpt, err := newPatchJson6902JSONTransformer(id, operations)
+	if err != nil {
+		t.Fatalf("unexpected error : %v", err)
+	}
+	err = jpt.Transform(base)
+	if err == nil {
+		t.Fatalf("expected error didn't happen")
+	}
+	if !strings.HasPrefix(err.Error(), "failed to apply json patch") || !strings.Contains(err.Error(), string(operations)) {
+		t.Fatalf("expected error didn't happen, but got %v", err)
+	}
+}