code: def test_stack():
      r = numpy.random.RandomState()
      r.seed(41)
      images = [r.uniform(size=(11, 13)) for _ in range(5)]
      workspace, module = make_workspace(
          cellprofiler.modules.graytocolor.SCHEME_STACK, images
      )
      module.run(workspace)
      output = workspace.image_set.get_image(
          OUTPUT_IMAGE_NAME
      ).pixel_data
      assert output.shape[:2] == images[0].shape
      assert output.shape[2] == len(images)
      for i, image in enumerate(images):
          numpy.testing.assert_array_almost_equal(
              output[:, :, i], image
          )
  
file_path: CellProfiler/tests/frontend/modules/test_graytocolor.py
imports: import numpy
  import six.moves
  import os
  import cellprofiler_core.image
  import cellprofiler_core.measurement
  import cellprofiler.modules.graytocolor
  import cellprofiler_core.object
  import cellprofiler_core.pipeline
  import cellprofiler_core.workspace
  import tests.frontend.modules
label_desc: Use image node_id 5 for calling a global function with example usage: test_stack() without return types