testing: use strings.Builder

Change-Id: Ied8a3019f1e21c0e74c798d2b1b279a606a38554
Reviewed-on: https://go-review.googlesource.com/c/go/+/428279
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/testing/fuzz.go

@@ -5,7 +5,6 @@
 package testing
 
 import (
-	"bytes"
 	"errors"
 	"flag"
 	"fmt"
@@ -14,6 +13,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"runtime"
+	"strings"
 	"time"
 )
 
@@ -379,7 +379,7 @@ func (f *F) Fuzz(ff any) {
 			// fuzz worker. This would become very verbose, particularly during
 			// minimization. Return the error instead, and let the caller deal
 			// with the output.
-			var buf bytes.Buffer
+			var buf strings.Builder
 			if ok := run(&buf, e); !ok {
 				return errors.New(buf.String())
 			}

src/testing/helper_test.go

@@ -5,13 +5,12 @@
 package testing
 
 import (
-	"bytes"
 	"regexp"
 	"strings"
 )
 
 func TestTBHelper(t *T) {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
 	t1 := &T{
 		common: common{
@@ -55,7 +54,7 @@ helperfuncs_test.go:67: 10
 }
 
 func TestTBHelperParallel(t *T) {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
 	t1 := &T{
 		common: common{

src/testing/iotest/logger_test.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"strings"
 	"testing"
 )
 
@@ -32,12 +33,12 @@ func TestWriteLogger(t *testing.T) {
 		log.SetOutput(olw)
 	}()
 
-	lOut := new(bytes.Buffer)
+	lOut := new(strings.Builder)
 	log.SetPrefix("lw: ")
 	log.SetOutput(lOut)
 	log.SetFlags(0)
 
-	lw := new(bytes.Buffer)
+	lw := new(strings.Builder)
 	wl := NewWriteLogger("write:", lw)
 	if _, err := wl.Write([]byte("Hello, World!")); err != nil {
 		t.Fatalf("Unexpectedly failed to write: %v", err)
@@ -64,7 +65,7 @@ func TestWriteLogger_errorOnWrite(t *testing.T) {
 		log.SetOutput(olw)
 	}()
 
-	lOut := new(bytes.Buffer)
+	lOut := new(strings.Builder)
 	log.SetPrefix("lw: ")
 	log.SetOutput(lOut)
 	log.SetFlags(0)
@@ -93,7 +94,7 @@ func TestReadLogger(t *testing.T) {
 		log.SetOutput(olw)
 	}()
 
-	lOut := new(bytes.Buffer)
+	lOut := new(strings.Builder)
 	log.SetPrefix("lr: ")
 	log.SetOutput(lOut)
 	log.SetFlags(0)
@@ -130,7 +131,7 @@ func TestReadLogger_errorOnRead(t *testing.T) {
 		log.SetOutput(olw)
 	}()
 
-	lOut := new(bytes.Buffer)
+	lOut := new(strings.Builder)
 	log.SetPrefix("lr: ")
 	log.SetOutput(lOut)
 	log.SetFlags(0)

src/testing/iotest/reader_test.go

@@ -26,7 +26,7 @@ func TestOneByteReader_nonEmptyReader(t *testing.T) {
 
 	b = make([]byte, 3)
 	// Read from obr until EOF.
-	got := new(bytes.Buffer)
+	got := new(strings.Builder)
 	for i := 0; ; i++ {
 		n, err = obr.Read(b)
 		if err != nil {
@@ -77,7 +77,7 @@ func TestHalfReader_nonEmptyReader(t *testing.T) {
 	}
 	// non empty read buffer
 	b = make([]byte, 2)
-	got := new(bytes.Buffer)
+	got := new(strings.Builder)
 	for i := 0; ; i++ {
 		n, err = hr.Read(b)
 		if err != nil {
@@ -190,7 +190,7 @@ func TestDataErrReader_nonEmptyReader(t *testing.T) {
 	der := DataErrReader(buf)
 
 	b := make([]byte, 3)
-	got := new(bytes.Buffer)
+	got := new(strings.Builder)
 	var n int
 	var err error
 	for {

src/testing/iotest/writer_test.go

@@ -5,7 +5,7 @@
 package iotest
 
 import (
-	"bytes"
+	"strings"
 	"testing"
 )
 
@@ -23,7 +23,7 @@ var truncateWriterTests = []struct {
 
 func TestTruncateWriter(t *testing.T) {
 	for _, tt := range truncateWriterTests {
-		buf := new(bytes.Buffer)
+		buf := new(strings.Builder)
 		tw := TruncateWriter(buf, tt.trunc)
 		n, err := tw.Write([]byte(tt.in))
 		if err != nil {

src/testing/sub_test.go

@@ -477,7 +477,7 @@ func TestTRun(t *T) {
 	for _, tc := range testCases {
 		t.Run(tc.desc, func(t *T) {
 			ctx := newTestContext(tc.maxPar, newMatcher(regexp.MatchString, "", ""))
-			buf := &bytes.Buffer{}
+			buf := &strings.Builder{}
 			root := &T{
 				common: common{
 					signal:  make(chan bool),
@@ -664,7 +664,7 @@ func TestBRun(t *T) {
 	for _, tc := range testCases {
 		t.Run(tc.desc, func(t *T) {
 			var ok bool
-			buf := &bytes.Buffer{}
+			buf := &strings.Builder{}
 			// This is almost like the Benchmark function, except that we override
 			// the benchtime and catch the failure result of the subbenchmark.
 			root := &B{