code: def test_masked_im(rgb_image):
      """Test that a masked image will be plotted using an alpha channel.
      Thus it should return an array that has a 4th dimension representing
      the alpha channel."""
  
      im, _ = rgb_image
      im_ma = ma.masked_where(im > 140, im)
  
      ax = plot_rgb(im_ma)
      im_plot = ax.get_images()[0].get_array()
      assert im_plot.shape[2] == 4
      plt.close()
  
imports: import numpy
  import numpy.ma
  import matplotlib.pyplot
  import pytest
  import rasterio
  from rasterio.plot import plotting_extent
  from earthpy.plot import plot_rgb, _stretch_im
  from earthpy.io import path_to_example
label_desc: Use image node_id 11 for calling a global function with example usage: test_masked_im(rgb_image) without return types