nclose := atomic.LoadInt32(&cl.closes)
	if nclose != 1 {
		t.Errorf("Close calls = %v; want 1", nclose)
	}
}

// Issue 20239: don't block in Serve if Shutdown is called first.
func TestServerShutdownThenServe(t *testing.T) {
	var srv Server
	cl := &countCloseListener{Listener: nil}
	srv.Shutdown(context.Background())
	got := srv.Serve(cl)
	if got != ErrServerClosed {