new_contents: import os, sys
  from collections import defaultdict
  import numpy as np
  from numpy.testing import assert_equal, assert_allclose
  from skan.csr import Skeleton
  
  from skan._testdata import (tinycycle, tinyline, skeleton0, skeleton1,
                              skeleton2, skeleton3d, topograph1d, skeleton4)
  
  
  def test_skeleton1_stats():
      skeleton = Skeleton(skeleton1)
      assert skeleton.paths.shape == (4, np.sum(skeleton1) + 1)
      paths_list = skeleton.paths_list()
      reference_paths = [
          [8, 6, 1, 2, 3, 4, 5, 7, 11, 10, 13],
          [8, 9, 13],
          [8, 12, 14],
          [13, 15, 16, 17]
      ]
      d0 = 1 + np.sqrt(2)
      reference_distances = [5 * d0, d0, d0, 1 + d0]
      for path in reference_paths:
          assert path in paths_list or path[::-1] in paths_list
      assert_allclose(sorted(skeleton.path_lengths()),
                      sorted(reference_distances))
  
  
  def test_tip_junction_edges():
      skeleton = Skeleton(skeleton4)
      reference_paths = [[1, 2], [2, 4, 5], [2, 7]]
      paths_list = skeleton.paths_list()
      for path in reference_paths:
          assert path in paths_list or path[::-1] in paths_list
  
subject: Add tests for new skeleton class