code: def test_vstack_sparse():
      res = vstack(
          [
              sp.csr_matrix([1, 2, 3]),
              sp.csr_matrix([4, 5, 6]),
          ]
      )
      assert res.shape == (2, 3)
      assert sp.issparse(res)
      assert np.array_equal(
          res.todense(), np.array([[1, 2, 3], [4, 5, 6]])
      )
  
file_path: eli5/tests/test_utils.py
imports: from __future__ import absolute_import
  import numpy
  import scipy.sparse
  from hypothesis import given, assume, settings, HealthCheck
  from hypothesis.strategies import integers
  from eli5.utils import argsort_k_largest, argsort_k_largest_positive, argsort_k_smallest, vstack
  from .utils import rnd_len_arrays
label_desc: Use image node_id 11 for calling a global function with example usage: test_vstack_sparse() without return types