new_contents: import pytest
  import cv2
  import numpy as np
  from plantcv.plantcv import hist_equalization
  
  
  def test_hist_equalization(test_data):
      # Read in test data
      img = cv2.imread(test_data.small_gray_img, -1)
      hist = hist_equalization(gray_img=img)
      assert np.average(hist) != np.average(img)
  
  
  def test_hist_equalization_bad_input(test_data):
      # Read in test data
      img = cv2.imread(test_data.small_rgb_img)
      with pytest.raises(RuntimeError):
          _ = hist_equalization(gray_img=img)
  
subject: Add hist_equalization tests module