code: def test_fss_single_point_slines():
      slines = [
          np.array([[1.0, 1.0, 1.0]]),
          np.array([[0.0, 1.0, 2.0]]),
      ]
      fss = FastStreamlineSearch(
          slines,
          max_radius=4.0,
          nb_mpts=4,
          bin_size=20.0,
          resampling=24,
          bidirectional=False,
      )
      res = fss.radius_search(slines, radius=4.0)
      # 2x2 matrix with 4 element
      assert_true(res.nnz == 4)
      mat = res.A
      dist = mean_euclidean_distance(slines[0], slines[1])
      assert_almost_equal(mat[0, 0], 0.0)
      assert_almost_equal(mat[1, 1], 0.0)
      assert_almost_equal(mat[1, 0], dist)
      assert_almost_equal(mat[0, 1], dist)
  
file_path: dipy/dipy/segment/tests/test_fss.py
imports: import numpy
  from dipy.data import get_fnames
  from dipy.io.streamline import load_tractogram
  from dipy.segment.fss import FastStreamlineSearch, nearest_from_matrix_row, nearest_from_matrix_col
  from dipy.segment.metric import mean_euclidean_distance
  from dipy.testing import assert_arrays_equal, assert_greater, assert_greater_equal, assert_true
  from numpy.testing import assert_almost_equal, assert_raises
label_desc: Use image node_id 4 for calling a global function with example usage: test_fss_single_point_slines() without return types