code: def test_graph():
      """Does graph neurons work on an empty image?"""
      workspace, module = make_workspace(
          numpy.zeros((20, 10), int),
          numpy.zeros((20, 10), bool),
          intensity_image=numpy.zeros((20, 10)),
          wants_graph=True,
      )
      module.prepare_run(workspace)
      module.run(workspace)
      edge_graph = read_graph_file(EDGE_FILE)
      vertex_graph = read_graph_file(VERTEX_FILE)
      assert len(edge_graph) == 0
      assert len(vertex_graph) == 0
  
imports: import os
  import tempfile
  import traceback
  import numpy
  import six.moves
  import cellprofiler_core.image
  import cellprofiler_core.measurement
  from cellprofiler_core.constants.measurement import GROUP_NUMBER, GROUP_INDEX, COLTYPE_FLOAT, COLTYPE_INTEGER
  import cellprofiler.modules.measureobjectskeleton
  import cellprofiler_core.object
  import cellprofiler_core.pipeline
  import cellprofiler_core.preferences
  import cellprofiler_core.setting
  import cellprofiler_core.workspace
  import tests.frontend.modules
label_desc: Use image node_id 13 for calling a global function with example usage: test_graph() without return types