code: def test_saves_source_from_file(tmp_path, src="graph spam { spam }"):
      path = tmp_path / "spam.gv"
      path.write_text(src)
      stat_before = path.stat()
  
      source = graphviz.Source.from_file(path)
      source.save()
  
      assert (
          path.stat().st_mtime == stat_before.st_mtime
      ), "file not overwritten"
      assert path.read_text() == src, "file contents unchanged"
      assert "".join(source) == f"{src}\n", "src with final newline"
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_saves_source_from_file(tmp_path, src) without return types