code: def test_nonexistent_edge():
      """Tests that attempting to contract a nonexistent edge raises an
      exception.
  
      """
      with pytest.raises(ValueError):
          G = nx.cycle_graph(4)
          nx.contracted_edge(G, (0, 2))
  
imports: import pytest
  import networkx
  from networkx.utils import arbitrary_element, edges_equal, nodes_equal
label_desc: Use image node_id 31 for calling a global function with example usage: test_nonexistent_edge() without return types