digraph G {
  subgraph cluster_os {
    style=filled;
    color=grey;
    label="Windows";

    subgraph cluster_python {
      label="Automation Tool/Python";
      color=lightgrey;
      HarnessCase -> HarnessController;
      HarnessCase -> OpenThreadController;
    }

    HarnessCase -> Chrome [label="selenium"];
    HarnessController -> "Thread Harness";
  }
  OpenThreadController -> DUT [label="serial port"];
}