code: def test_get_sub_runs():
      wf = Workflow()
      assert len(wf.get_sub_runs()) == 0
  
file_path: dipy/dipy/workflows/tests/test_workflow.py
imports: import os
  import time
  from os.path import join
  from tempfile import TemporaryDirectory
  import numpy.testing
  from dipy.data import get_fnames
  from dipy.workflows.segment import MedianOtsuFlow
  from dipy.workflows.workflow import Workflow
label_desc: Use image node_id 2 for calling a global function with example usage: test_get_sub_runs() without return types