code: def test_graph_depth_first_trivial_graph():
      csgraph = np.array([[0]])
      csgraph = csgraph_from_dense(csgraph, null_value=0)
  
      bfirst = np.array([[0]])
  
      for directed in [True, False]:
          bfirst_test = depth_first_tree(csgraph, 0, directed)
          assert_array_almost_equal(
              csgraph_to_dense(bfirst_test), bfirst
          )
  
file_path: catboost/contrib/python/scipy/py2/scipy/sparse/csgraph/tests/test_traversal.py
imports: from __future__ import division, print_function, absolute_import
  import numpy
  from numpy.testing import assert_array_almost_equal
  from scipy.sparse.csgraph import breadth_first_tree, depth_first_tree, csgraph_to_dense, csgraph_from_dense
label_desc: Use image node_id 4 for calling a global function with example usage: test_graph_depth_first_trivial_graph() without return types