class_docstr: Unit tests for the :func:`~networkx.node_boundary` function.
class_docstr_tok: ["Unit","tests","for","the",":","func",":","`","~networkx.node_boundary","`","function","."]
docstr: Tests that the null graph has empty node boundaries.
docstr_tok: ["Tests","that","the","null","graph","has","empty","node","boundaries","."]
code: def test_null_graph(self):
      """Tests that the null graph has empty node boundaries."""
      null = nx.null_graph()
      assert nx.node_boundary(null, []) == set()
      assert nx.node_boundary(null, [], []) == set()
      assert nx.node_boundary(null, [1, 2, 3]) == set()
      assert nx.node_boundary(null, [1, 2, 3], [4, 5, 6]) == set()
      assert nx.node_boundary(null, [1, 2, 3], [3, 4, 5]) == set()
  
imports: from itertools import combinations
  import pytest
  import networkx
  from networkx import convert_node_labels_to_integers
  from networkx.utils import edges_equal
label_desc: Use image node_id 1 for calling the TestNodeBoundary obj's underlying member method code with example usage: obj.test_null_graph() without return types