bytes: deflake TestGrow by using testing.AllocsPerRun

Fixes #36695

Change-Id: I4392246015252018b49f321a5a839cc68cc611d7
GitHub-Last-Rev: c2fb1f7ddbe9b80059eed69f31781abe0a1db185
GitHub-Pull-Request: golang/go#36732
Reviewed-on: https://go-review.googlesource.com/c/go/+/216237
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/bytes/buffer_test.go b/src/bytes/buffer_test.go
index 7626d277d4f489251303a53022ac258db89fdf13..fec5ef8a35f637dacd1c95b9ad3034b6f3559308 100644 (file)
--- a/src/bytes/buffer_test.go
+++ b/src/bytes/buffer_test.go
@@ -8,7 +8,6 @@ import (
        . "bytes"
        "io"
        "math/rand"
-       "runtime"
        "testing"
        "unicode/utf8"
 )
@@ -495,20 +494,20 @@ func TestGrow(t *testing.T) {
        x := []byte{'x'}
        y := []byte{'y'}
        tmp := make([]byte, 72)
-       for _, startLen := range []int{0, 100, 1000, 10000, 100000} {
-               xBytes := Repeat(x, startLen)
-               for _, growLen := range []int{0, 100, 1000, 10000, 100000} {
+       for _, growLen := range []int{0, 100, 1000, 10000, 100000} {
+               for _, startLen := range []int{0, 100, 1000, 10000, 100000} {
+                       xBytes := Repeat(x, startLen)
+
                        buf := NewBuffer(xBytes)
                        // If we read, this affects buf.off, which is good to test.
                        readBytes, _ := buf.Read(tmp)
-                       buf.Grow(growLen)
                        yBytes := Repeat(y, growLen)
+                       allocs := testing.AllocsPerRun(100, func() {
+                               buf.Grow(growLen)
+                               buf.Write(yBytes)
+                       })
                        // Check no allocation occurs in write, as long as we're single-threaded.
-                       var m1, m2 runtime.MemStats
-                       runtime.ReadMemStats(&m1)
-                       buf.Write(yBytes)
-                       runtime.ReadMemStats(&m2)
-                       if runtime.GOMAXPROCS(-1) == 1 && m1.Mallocs != m2.Mallocs {
+                       if allocs != 0 {
                                t.Errorf("allocation occurred during write")
                        }
                        // Check that buffer has correct data.