new_contents: import unittest
  
  import mock
  
  import numpy
  import scipy.special
  
  from enable.api import AbstractWindow
  from chaco.api import (
      CMapImagePlot, DataRange1D, DataRange2D, GridDataSource, GridMapper,
      ImageData)
  from chaco.default_colormaps import Spectral
  
  class TestCMapImagePlot(unittest.TestCase):
  
      def test_redraw_on_color_mapper_update(self):
          # regression check for https://github.com/enthought/chaco/issues/220
          npoints = 200
  
          xs = numpy.linspace(-2 * numpy.pi, +2 * numpy.pi, npoints)
          ys = numpy.linspace(-1.5*numpy.pi, +1.5*numpy.pi, npoints)
          x, y = numpy.meshgrid(xs, ys)
          z = scipy.special.jn(2, x)*y*x
  
          index = GridDataSource(xdata=xs, ydata=ys)
          index_mapper = GridMapper(range=DataRange2D(index))
  
          color_source = ImageData(data=z, value_depth=1)
          color_mapper = Spectral(DataRange1D(color_source))
  
          cmap_plot = CMapImagePlot(
              index=index,
              index_mapper=index_mapper,
              value=color_source,
              value_mapper=color_mapper,
          )
          cmap_plot._window = window = mock.Mock(spec=AbstractWindow)
  
          #when
          cmap_plot.color_mapper.updated = True
  
          # Then
          window.redraw.assert_called_once_with()
  
  if __name__ == "__main__":
      unittest.main()
  
subject: add a test for issue #220