docs: def validate_basic_smoother():
      """Run Friedman's test from Figure 2b."""
      x, y = sort_data(*smoother_friedman82.build_sample_smoother_problem_friedman82())
      plt.figure()
      # plt.plot(x, y, '.', label='Data')
      for span in smoother.DEFAULT_SPANS:
          my_smoother = smoother.perform_smooth(x, y, span)
          friedman_smooth, _resids = run_friedman_smooth(x, y, span)
          plt.plot(x, my_smoother.smooth_result, '.-', label='pyace span = {0}'.format(span))
          plt.plot(x, friedman_smooth, '.-', label='Friedman span = {0}'.format(span))
      finish_plot()