net/http/httptrace: test the order of hooks when ctx has multi ClientTraces

Change-Id: I95cae14bb5561947ada9577fb05053f93321a4a8
Reviewed-on: https://go-review.googlesource.com/27400
Run-TryBot: Jaana Burcu Dogan <jbd@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/httptrace/trace_test.go

@@ -6,9 +6,36 @@ package httptrace
 
 import (
 	"bytes"
+	"context"
 	"testing"
 )
 
+func TestWithClientTrace(t *testing.T) {
+	var buf bytes.Buffer
+	connectStart := func(b byte) func(network, addr string) {
+		return func(network, addr string) {
+			buf.WriteByte(b)
+		}
+	}
+
+	ctx := context.Background()
+	oldtrace := &ClientTrace{
+		ConnectStart: connectStart('O'),
+	}
+	ctx = WithClientTrace(ctx, oldtrace)
+	newtrace := &ClientTrace{
+		ConnectStart: connectStart('N'),
+	}
+	ctx = WithClientTrace(ctx, newtrace)
+	trace := ContextClientTrace(ctx)
+
+	buf.Reset()
+	trace.ConnectStart("net", "addr")
+	if got, want := buf.String(), "NO"; got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}
+
 func TestCompose(t *testing.T) {
 	var buf bytes.Buffer
 	var testNum int