code: def test_retrieval_sparse(self):
      for k in range(100):
          self.engine.clean_all_buckets()
          x = scipy.sparse.rand(1000, 1, density=0.05)
          x_data = "data"
          self.engine.store_vector(x, x_data)
          n = self.engine.neighbours(x)
          y, y_data, y_distance = n[0]
          normalized_x = unitvec(x)
          delta = 0.000000001
          self.assertAlmostEqual(
              numpy.abs((normalized_x - y)).max(), 0, delta=delta
          )
          self.assertEqual(y_data, x_data)
          self.assertAlmostEqual(y_distance, 0.0, delta=delta)
  
imports: import itertools
  import unittest
  import numpy
  import scipy
  from future.builtins import range
  from nearpy import Engine
  from nearpy.utils.utils import unitvec
  from nearpy.hashes import UniBucket
label_desc: Use image node_id 4 for calling the TestEngine obj's underlying member method code with example usage: obj.test_retrieval_sparse() without return types