text: """module to start pure mpl-backend viewer"""
  import matplotlib.pyplot as plt
  import numpy as np
  from xpdview.cross_2d import StackViewer, CrossSection
  from xpdview.waterfall import Waterfall
  
  # def data list to test
  img_data_list = []
  key_list = []
  int_data_list = []
  x = np.linspace(0, 2*np.pi, 200)
  for i in range(5):
      key_list.append(str(i))
      img_data_list.append(np.random.rand(50, 50))
      int_data_list.append((x, np.sin(x)))
  
  # init
  viewer_fig = plt.figure('test_viewer')  # let mpl decide backend
  cross_section = CrossSection(viewer_fig)
  stack_viewer = StackViewer(cross_section, img_data_list=img_data_list,
                             key_list=key_list)
  waterfall_fig = plt.figure('test_waterfall')  # let mpl decide backend
  waterfall = Waterfall(fig=waterfall_fig, key_list=key_list,
                        int_data_list=int_data_list,
                        unit=('x_unit', 'y_unit'))
  plt.show()
  