old_contents: import unittest
  
  import numpy as np
  
  from laserchicken import read_las
  from laserchicken.feature_extractor.mean_z_feature_extractor import MeanZFeatureExtractor
  
  
  class TestHeightStatisticsFeatureExtractor(unittest.TestCase):
      def test_height_stats(self):
          pc_in = read_las.read("testdata/AHN2.las")
          neighborhood = [89664, 23893, 30638, 128795, 62052, 174453, 29129, 17127, 128215, 29667, 116156, 119157, 98591,
                          7018,
                          61494, 65194, 117931, 62971, 10474, 90322]
          mean_z = MeanZFeatureExtractor().extract(pc_in, neighborhood, None, None, None)
          np.testing.assert_allclose(mean_z, 1.3779999737739566)
  
      def test_height_stats_without_neighbors(self):
          pc_in = read_las.read("testdata/AHN2.las")
          neighborhood = []
          mean_z = MeanZFeatureExtractor().extract(pc_in, neighborhood, pc_in, None, None)
          assert np.isnan(mean_z)
  
new_contents: import unittest
  
  import numpy as np
  
  from laserchicken import read_las
  from laserchicken.feature_extractor.mean_z_feature_extractor import MeanZFeatureExtractor
  
  
  class TestMeanZFeatureExtractor(unittest.TestCase):
      def test_height_stats(self):
          pc_in = read_las.read("testdata/AHN2.las")
          neighborhood = [89664, 23893, 30638, 128795, 62052, 174453, 29129, 17127, 128215, 29667, 116156, 119157, 98591,
                          7018,
                          61494, 65194, 117931, 62971, 10474, 90322]
          mean_z = MeanZFeatureExtractor().extract(pc_in, neighborhood, None, None, None)
          np.testing.assert_allclose(mean_z, 1.3779999737739566)
  
      def test_height_stats_without_neighbors(self):
          pc_in = read_las.read("testdata/AHN2.las")
          neighborhood = []
          mean_z = MeanZFeatureExtractor().extract(pc_in, neighborhood, pc_in, None, None)
          assert np.isnan(mean_z)
  
subject: fix test class name