code: func Window(window uint16) TransportChecker {
  	return func(t *testing.T, h header.Transport) {
  		tcp, ok := h.(header.TCP)
  		if !ok {
  			return
  		}
  
  		if w := tcp.WindowSize(); w != window {
  			t.Errorf("Bad window, got 0x%x, want 0x%x", w, window)
  		}
  	}
  }
docs: // Window creates a checker that checks the tcp window.