testing: add AllocsPerRun

This CL also replaces similar loops in other stdlib
package tests with calls to AllocsPerRun.

Fixes #4461.

R=minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7002055

1 files changed, 4 insertions, 13 deletions

diff --git a/src/pkg/path/filepath/path_test.go b/src/pkg/path/filepath/path_test.go
index bd251a4ebb..84609c4bfc 100644
--- a/src/pkg/path/filepath/path_test.go
+++ b/src/pkg/path/filepath/path_test.go
@@ -91,7 +91,6 @@ var wincleantests = []PathTest{
 }
 
 func TestClean(t *testing.T) {
-	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
 	tests := cleantests
 	if runtime.GOOS == "windows" {
 		for i := range tests {
@@ -108,20 +107,12 @@ func TestClean(t *testing.T) {
 		}
 	}
 
-	var ms runtime.MemStats
-	runtime.ReadMemStats(&ms)
-	allocs := -ms.Mallocs
-	const rounds = 100
-	for i := 0; i < rounds; i++ {
-		for _, test := range tests {
-			filepath.Clean(test.result)
+	for _, test := range tests {
+		allocs := testing.AllocsPerRun(100, func() { filepath.Clean(test.result) })
+		if allocs > 0 {
+			t.Errorf("Clean(%q): %v allocs, want zero", test.result, allocs)
 		}
 	}
-	runtime.ReadMemStats(&ms)
-	allocs += ms.Mallocs
-	if allocs >= rounds {
-		t.Errorf("Clean cleaned paths: %d allocations per test round, want zero", allocs/rounds)
-	}
 }
 
 const sep = filepath.Separator