code: def test_undirected_node_contraction():
      """Tests for node contraction in an undirected graph."""
      G = nx.cycle_graph(4)
      actual = nx.contracted_nodes(G, 0, 1)
      expected = nx.cycle_graph(3)
      expected.add_edge(0, 0)
      assert nx.is_isomorphic(actual, expected)
  
imports: import pytest
  import networkx
  from networkx.utils import arbitrary_element, edges_equal, nodes_equal
label_desc: Use image node_id 19 for calling a global function with example usage: test_undirected_node_contraction() without return types