http2: report an error if goroutines outlive serverTester tests

Change-Id: Icd2152b4bddacf12120be16c32c8c2d52d235fbd
Reviewed-on: https://go-review.googlesource.com/c/net/+/589075
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

http2/clientconn_test.go

@@ -14,7 +14,6 @@ import (
 	"io"
 	"net/http"
 	"reflect"
-	"runtime"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -513,12 +512,7 @@ func newTestTransport(t *testing.T, opts ...func(*Transport)) *testTransport {
 		if len(tt.ccs) > 0 {
 			t.Fatalf("%v test ClientConns created, but not examined by test", len(tt.ccs))
 		}
-		if count := tt.group.Count(); count != 1 {
-			buf := make([]byte, 16*1024)
-			n := runtime.Stack(buf, true)
-			t.Logf("stacks:\n%s", buf[:n])
-			t.Fatalf("%v goroutines still running after test completed, expect 1", count)
-		}
+		tt.group.Close(t)
 	})
 
 	return tt

http2/server_test.go

@@ -150,6 +150,10 @@ var optQuiet = func(server *http.Server) {
 func newServerTester(t testing.TB, handler http.HandlerFunc, opts ...interface{}) *serverTester {
 	t.Helper()
 	g := newSynctest(time.Date(2000, 1, 1, 0, 0, 0, 0, time.UTC))
+	t.Cleanup(func() {
+		g.Close(t)
+	})
+
 	h1server := &http.Server{}
 	h2server := &Server{
 		group: g,
@@ -191,6 +195,7 @@ func newServerTester(t testing.TB, handler http.HandlerFunc, opts ...interface{}
 
 	t.Cleanup(func() {
 		st.Close()
+		g.AdvanceTime(goAwayTimeout) // give server time to shut down
 	})
 
 	connc := make(chan *serverConn)

http2/sync_test.go

@@ -11,6 +11,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"testing"
 	"time"
 )
 
@@ -58,6 +59,16 @@ func (g *synctestGroup) Count() int {
 	return count
 }
 
+// Close calls t.Fatal if the group contains any running goroutines.
+func (g *synctestGroup) Close(t testing.TB) {
+	if count := g.Count(); count != 1 {
+		buf := make([]byte, 16*1024)
+		n := runtime.Stack(buf, true)
+		t.Logf("stacks:\n%s", buf[:n])
+		t.Fatalf("%v goroutines still running after test completed, expect 1", count)
+	}
+}
+
 // Wait blocks until every goroutine in the group and their direct children are idle.
 func (g *synctestGroup) Wait() {
 	for i := 0; ; i++ {