net/rpc/jsonrpc: add temporarily-disabled failing test

To be enabled by https://golang.org/cl/71230045/

Update #7442

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/69860056

src/pkg/net/rpc/jsonrpc/all_test.go

@@ -5,6 +5,7 @@
 package jsonrpc
 
 import (
+	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -12,6 +13,7 @@ import (
 	"io/ioutil"
 	"net"
 	"net/rpc"
+	"strings"
 	"testing"
 )
 
@@ -202,6 +204,40 @@ func TestMalformedOutput(t *testing.T) {
 	}
 }
 
+func TestServerErrorHasNullResult(t *testing.T) {
+	t.Skip("Known failing test; Issue 7442")
+	var out bytes.Buffer
+	sc := NewServerCodec(struct {
+		io.Reader
+		io.Writer
+		io.Closer
+	}{
+		Reader: strings.NewReader(`{"method": "Arith.Add", "id": "123", "params": []}`),
+		Writer: &out,
+		Closer: ioutil.NopCloser(nil),
+	})
+	r := new(rpc.Request)
+	if err := sc.ReadRequestHeader(r); err != nil {
+		t.Fatal(err)
+	}
+	const valueText = "the value we don't want to see"
+	const errorText = "some error"
+	err := sc.WriteResponse(&rpc.Response{
+		ServiceMethod: "Method",
+		Seq:           1,
+		Error:         errorText,
+	}, valueText)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(out.String(), errorText) {
+		t.Fatalf("Response didn't contain expected error %q: %s", errorText, &out)
+	}
+	if strings.Contains(out.String(), valueText) {
+		t.Errorf("Response contains both an error and value: %s", &out)
+	}
+}
+
 func TestUnexpectedError(t *testing.T) {
 	cli, srv := myPipe()
 	go cli.PipeWriter.CloseWithError(errors.New("unexpected error!")) // reader will get this error