code: def test_otsu3_low():
      """Test the three-class otsu, weighted variance middle = background"""
      numpy.random.seed(0)
      image = numpy.hstack(
          (
              numpy.random.exponential(1.5, size=300),
              numpy.random.poisson(15, size=300),
              numpy.random.poisson(30, size=300),
          )
      ).astype(numpy.float32)
      image.shape = (30, 30)
      image = centrosome.filter.stretch(image)
      t1, threshold = skimage.filters.threshold_multiotsu(
          image, nbins=128
      )
      workspace, module = make_workspace(image)
      module.threshold_scope.value = (
          cellprofiler.modules.threshold.TS_GLOBAL
      )
      module.global_operation.value = centrosome.threshold.TM_OTSU
      module.two_class_otsu.value = (
          cellprofiler.modules.threshold.O_THREE_CLASS
      )
      module.assign_middle_to_foreground.value = (
          cellprofiler.modules.threshold.O_BACKGROUND
      )
      module.run(workspace)
      m = workspace.measurements
      m_threshold = m[
          "Image",
          FF_ORIG_THRESHOLD % module.y_name.value,
      ]
      assert round(abs(m_threshold - threshold), 7) == 0
  
imports: import io
  import centrosome.filter
  import centrosome.otsu
  import centrosome.threshold
  import numpy
  import numpy.testing
  import skimage.filters
  import skimage.filters.rank
  import skimage.morphology
  import cellprofiler.modules.threshold
  import cellprofiler_core.image
  import cellprofiler_core.measurement
  import cellprofiler_core.module
  import cellprofiler_core.object
  import cellprofiler_core.pipeline
  import cellprofiler_core.preferences
  import cellprofiler_core.workspace
  from cellprofiler_core.constants.measurement import FF_ORIG_THRESHOLD
  from cellprofiler_core.constants.module._identify import TS_GLOBAL
  import cellprofiler_library.modules
  import cellprofiler_library.functions
  import tests.frontend.modules
label_desc: Use image node_id 15 for calling a global function with example usage: test_otsu3_low() without return types