code: def test_length(rng):
      # Generate a simulated bundle of fibers:
      n_streamlines = 50
      n_pts = 100
      t = np.linspace(-10, 10, n_pts)
  
      bundle = []
      for i in np.linspace(3, 5, n_streamlines):
          pts = np.vstack(
              (np.cos(2 * t / np.pi), np.zeros(t.shape) + i, t)
          ).T
          bundle.append(pts)
  
      start = rng.integers(10, 30, n_streamlines)
      end = rng.integers(60, 100, n_streamlines)
  
      bundle = [
          10 * streamline[start[i] : end[i]]
          for (i, streamline) in enumerate(bundle)
      ]
  
      bundle_lengths = length(bundle)
      for idx, this_length in enumerate(bundle_lengths):
          npt.assert_equal(this_length, metrics.length(bundle[idx]))
  
imports: import warnings
  import numpy
  import pytest
  from dipy.tracking import metrics
  from dipy.tracking.streamline import transform_streamlines
  from dipy.tracking.utils import connectivity_matrix, density_map, length, ndbincount, reduce_labels, seeds_from_mask, random_seeds_from_mask, target, target_line_based, unique_rows, near_roi, reduce_rois, path_length, _min_at, max_angle_from_curvature, min_radius_curvature_from_angle
  from dipy.tracking._utils import _to_voxel_coordinates
  from dipy.tracking.vox2track import streamline_mapping
  import numpy.testing
  from dipy.testing import assert_true
  from dipy.testing.decorators import set_random_number_generator
label_desc: Use image node_id 13 for calling a global function with example usage: test_length(rng) without return types