code: def test_simple_graph(tmpdir):
      try:
          from graphviz import Digraph
      except:
          pytest.skip("Skip because graphviz is not installed.")
      from nnabla.experimental.viewers import SimpleGraph
  
      sg = SimpleGraph()
  
      nn.clear_parameters()
      x = nn.Variable((2, 3, 4, 4))
      with nn.parameter_scope("c1"):
          h = PF.convolution(x, 8, (3, 3), pad=(1, 1))
          h = F.relu(PF.batch_normalization(h))
      with nn.parameter_scope("f1"):
          y = PF.affine(h, 10)
      g = sg.create_graphviz_digraph(y)
      assert isinstance(g, Digraph)
      tmpdir.ensure(dir=True)
      # fpath = tmpdir.join('graph').strpath
      fpath = "tmp-draw"
      sg.save(y, fpath, format="png")
  
imports: import pytest
  import nnabla
  import nnabla.functions
  import nnabla.parametric_functions
label_desc: Use image node_id 1 for calling a global function with example usage: test_simple_graph(tmpdir) without return types