testing: convert numFailed to atomic type

Change-Id: Ic3464e95ad8901df5477d7717760b8c6d08ce97b
Reviewed-on: https://go-review.googlesource.com/c/go/+/426078
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/testing/fuzz.go

@@ -14,7 +14,6 @@ import (
 	"path/filepath"
 	"reflect"
 	"runtime"
-	"sync/atomic"
 	"time"
 )
 
@@ -615,7 +614,7 @@ func fRunner(f *F, fn func(*F)) {
 		// the original panic should still be
 		// clear.
 		if f.Failed() {
-			atomic.AddUint32(&numFailed, 1)
+			numFailed.Add(1)
 		}
 		err := recover()
 		if err == nil {

src/testing/testing.go

@@ -443,7 +443,7 @@ var (
 	cpuList     []int
 	testlogFile *os.File
 
-	numFailed uint32 // number of test failures
+	numFailed atomic.Uint32 // number of test failures
 )
 
 type chattyPrinter struct {
@@ -1312,7 +1312,7 @@ func tRunner(t *T, fn func(t *T)) {
 	// a signal saying that the test is done.
 	defer func() {
 		if t.Failed() {
-			atomic.AddUint32(&numFailed, 1)
+			numFailed.Add(1)
 		}
 
 		if t.raceErrors+race.Errors() > 0 {
@@ -2064,5 +2064,5 @@ func parseCpuList() {
 }
 
 func shouldFailFast() bool {
-	return *failFast && atomic.LoadUint32(&numFailed) > 0
+	return *failFast && numFailed.Load() > 0
 }