Properly fix brittle test

Unlike cf868f, this should fix the brittle test issue.

format.go

@@ -32,15 +32,7 @@ func writeFormat(w io.Writer, s stackCounter, f Format, hz int) error {
 }
 
 func writeFolded(w io.Writer, s stackCounter) error {
-	// Sort the stacks since I suspect that Brendan Gregg's FlameGraph tool's
-	// display order is influenced by it.
-	var stacks []string
-	for stack := range s {
-		stacks = append(stacks, stack)
-	}
-	sort.Strings(stacks)
-
-	for _, stack := range stacks {
+	for _, stack := range sortedKeys(s) {
 		count := s[stack]
 		if _, err := fmt.Fprintf(w, "%s %d\n", stack, count); err != nil {
 			return err
@@ -99,3 +91,12 @@ func toPprof(s stackCounter, hz int) *profile.Profile {
 	}
 	return p
 }
+
+func sortedKeys(s stackCounter) []string {
+	var keys []string
+	for stack := range s {
+		keys = append(keys, stack)
+	}
+	sort.Strings(keys)
+	return keys
+}

pprof.go

@@ -25,7 +25,8 @@ func toProfile(s stackCounter, hz int) *profile.Profile {
 		},
 	}
 
-	for stack, count := range s {
+	for _, stack := range sortedKeys(s) {
+		count := s[stack]
 		sample := &profile.Sample{
 			Value: []int64{
 				int64(count),

pprof_test.go

@@ -20,12 +20,12 @@ func Test_toProfile(t *testing.T) {
 Period: 0
 Samples:
 samples/count time/nanoseconds
-          2   20202020: 1 2 
-          1   10101010: 3 
+          1   10101010: 1 
+          2   20202020: 2 3 
 Locations
      1: 0x0 M=1 foo :0 s=0()
-     2: 0x0 M=1 bar :0 s=0()
-     3: 0x0 M=1 foo :0 s=0()
+     2: 0x0 M=1 foo :0 s=0()
+     3: 0x0 M=1 bar :0 s=0()
 Mappings
 1: 0x0/0x0/0x0   [FN]
 `)