code: def setUp(self):
      self.documents = [
          ["cat", "dog", "mouse"],
          ["cat", "lion"],
          ["cat", "lion"],
      ]
      self.dictionary = Dictionary(self.documents)
      self.k1, self.b = 1.5, 0.75
  
      def get_idf(word):
          frequency = sum(
              map(lambda document: word in document, self.documents)
          )
          return math.log(
              1.0
              + (len(self.documents) - frequency + 0.5)
              / (frequency + 0.5)
          )
  
      self.expected_dog_idf = get_idf("dog")
      self.expected_cat_idf = get_idf("cat")
      self.expected_mouse_idf = get_idf("mouse")
      self.expected_lion_idf = get_idf("lion")
  
imports: from collections import defaultdict
  import math
  import unittest
  from gensim.models.bm25model import BM25ABC
  from gensim.models import OkapiBM25Model, LuceneBM25Model, AtireBM25Model
  from gensim.corpora import Dictionary
label_desc: Use image node_id 1 for calling the LuceneBM25ModelTest obj's underlying member method code with example usage: obj.setUp() and returns: math