code: def test_concatenate_sparse(self):
      x = csr_matrix(np.array([[0, 1], [1, 0], [1, 1]]))
      y = csr_matrix(np.array([[1, 1], [1, 0], [0, 1]]))
  
      result = concatenate(x, y)
      expected = csr_matrix(
          np.array([[0, 1], [1, 0], [1, 1], [1, 1], [1, 0], [0, 1]])
      )
  
      assert_csr_matrix_equal(expected, result)
  
imports: import unittest
  import numpy
  from numpy.testing import assert_array_equal
  from scipy.sparse import csr_matrix
  from small_text.base import LABEL_IGNORED, LABEL_UNLABELED
  from small_text.utils.labels import concatenate, csr_to_list, get_flattened_unique_labels, get_ignored_labels_mask, get_num_labels, list_to_csr, remove_by_index
  from tests.utils.testing import assert_csr_matrix_equal
  from tests.utils.datasets import random_sklearn_dataset
label_desc: Use image node_id 4 for calling the LabelUtilsTest obj's underlying member method code with example usage: obj.test_concatenate_sparse() without return types