code: def test_alpha(image_array_2bands):
      """Test that the alpha param returns a plot with the correct alpha."""
      alpha_val = 0.5
      alpha_ax = ep.plot_bands(
          image_array_2bands, cols=2, alpha=alpha_val
      )
      for i in range(len(alpha_ax)):
          assert alpha_ax[i].get_images()[0].get_alpha() == alpha_val
  
imports: import pytest
  import matplotlib.pyplot
  import matplotlib.colors
  import earthpy.plot
  import numpy
label_desc: Use image node_id 17 for calling a global function with example usage: test_alpha(image_array_2bands) without return types