docstr: should return only edges whose origin is unknown
docstr_tok: ["should","return","only","edges","whose","origin","is","unknown"]
code: def test_edge_expert_property(self):
      """should return only edges whose origin is unknown"""
  
      sm = StructureModel()
      sm.add_edge(1, 2, origin="unknown")
      sm.add_edge(1, 3, origin="learned")
      sm.add_edge(1, 4, origin="expert")
  
      assert sm.edges_with_origin("expert") == [(1, 4)]
  
imports: import pytest
  from networkx.exception import NodeNotFound
  from causalnex.structure import StructureModel
label_desc: Use image node_id 5 for calling the TestStructureModel obj's underlying member method code with example usage: obj.test_edge_expert_property() without return types