code: def test_eulerian_path_straight_link(self):
      G = nx.DiGraph()
      result = [(1, 2), (2, 3), (3, 4), (4, 5)]
      G.add_edges_from(result)
      assert result == list(nx.eulerian_path(G))
      assert result == list(nx.eulerian_path(G, source=1))
      with pytest.raises(nx.NetworkXError):
          list(nx.eulerian_path(G, source=3))
      with pytest.raises(nx.NetworkXError):
          list(nx.eulerian_path(G, source=4))
      with pytest.raises(nx.NetworkXError):
          list(nx.eulerian_path(G, source=5))
  
imports: import collections
  import pytest
  import networkx
label_desc: Use image node_id 2 for calling the TestEulerianPath obj's underlying member method code with example usage: obj.test_eulerian_path_straight_link() without return types