docstr: Test rank returns expected value for distinct and identical nodes.
code: def test_rank(self):
      """Test rank returns expected value for distinct and identical nodes."""
      self.assertEqual(self.vectors.rank("dog.n.01", "dog.n.01"), 1)
      self.assertEqual(
          self.vectors.rank("dog.n.01", "carnivore.n.01"), 3
      )
  
imports: import logging
  import os
  import tempfile
  import unittest
  import numpy
  from gensim.models.poincare import PoincareRelations, PoincareModel, PoincareKeyedVectors
  from gensim.test.utils import datapath
label_desc: Use image node_id 21 for calling the TestPoincareKeyedVectors obj's underlying member method code with example usage: obj.test_rank() without return types