class_docstr: Unit tests for the chain decomposition function.
code: def test_barbell_graph(self):
      # The (3, 0) barbell graph has two triangles joined by a single edge.
      G = nx.barbell_graph(3, 0)
      chains = list(nx.chain_decomposition(G, root=0))
      expected = [[(0, 1), (1, 2), (2, 0)], [(3, 4), (4, 5), (5, 3)]]
      assert len(chains) == len(expected)
      for chain in chains:
          self.assertContainsChain(chain, expected)
  
file_path: networkx/networkx/algorithms/tests/test_chains.py
imports: from itertools import cycle, islice
  import pytest
  import networkx
label_desc: Use image node_id 3 for calling the TestChainDecomposition obj's underlying member method code with example usage: obj.test_barbell_graph() without return types