code: func SrcPort(port uint16) TransportChecker {
  	return func(t *testing.T, h header.Transport) {
  		t.Helper()
  
  		if p := h.SourcePort(); p != port {
  			t.Errorf("Bad source port, got %v, want %v", p, port)
  		}
  	}
  }
docs: // SrcPort creates a checker that checks the source port.