code: def test_tril(self):
      for A in self.cases:
          B = A.toarray()
          for k in [-3, -2, -1, 0, 1, 2, 3]:
              assert_equal(
                  extract.tril(A, k=k).toarray(), np.tril(B, k=k)
              )
  
file_path: catboost/contrib/python/scipy/py2/scipy/sparse/tests/test_extract.py
imports: from __future__ import division, print_function, absolute_import
  from numpy.testing import assert_equal
  from scipy.sparse import csr_matrix
  import numpy
  from scipy.sparse import extract
label_desc: Use image node_id 3 for calling the TestExtract obj's underlying member method code with example usage: obj.test_tril() without return types