code: def _get_model(self):
      return implicit.nearest_neighbours.BM25Recommender(K=50)
  
file_path: implicit/tests/knn_test.py
imports: import unittest
  import numpy
  import pytest
  from recommender_base_test import RecommenderBaseTestMixin
  from scipy.sparse import csr_matrix
  import implicit
label_desc: Use image node_id 1 for calling the BM25Test obj's underlying member method code with example usage: obj._get_model() and returns: implicit