class_docstr: Mixin to test a bunch of common functionality in models
  deriving from RecommenderBase
code: def test_similar_items(self):
      model = self._get_model()
      user_items = get_checker_board(256)
      item_users = user_items.T.tocsr()
      model.fit(user_items, show_progress=False)
  
      for itemid in range(50):
          ids, scores = model.similar_items(itemid, N=10)
          for r in ids:
              self.assertEqual(r % 2, itemid % 2)
  
          try:
              (
                  recalculated_ids,
                  recalculated_scores,
              ) = model.similar_items(
                  itemid, N=10, item_users=item_users[itemid]
              )
              assert np.allclose(ids, recalculated_ids)
              assert np.allclose(scores, recalculated_scores)
          except NotImplementedError:
              continue
  
imports: import os
  import pickle
  import random
  import tempfile
  import numpy
  import pytest
  from numpy.testing import assert_array_equal
  from scipy.sparse import coo_matrix, csr_matrix
  from implicit.evaluation import precision_at_k
  from implicit.nearest_neighbours import ItemItemRecommender
  from implicit.utils import ParameterWarning
label_desc: Use image node_id 9 for calling the RecommenderBaseTestMixin obj's underlying member method code with example usage: obj.test_similar_items() without return types