code: def test_len():
      n = 10
      elements = get_elements(n)
      dis = DisjointSet(elements)
      assert len(dis) == n
  
      dis.add("dummy")
      assert len(dis) == n + 1
  
file_path: catboost/contrib/python/scipy/py3/scipy/cluster/tests/test_disjoint_set.py
imports: import pytest
  from pytest import raises
  import numpy
  from scipy.cluster.hierarchy import DisjointSet
  import string
label_desc: Use image node_id 4 for calling a global function with example usage: test_len() without return types