code: def test_GraphMLWriter_add_graphs(self):
      gmlw = GraphMLWriter()
      G = self.simple_directed_graph
      H = G.copy()
      gmlw.add_graphs([G, H])
  
imports: import io
  import pytest
  import networkx
  from networkx.readwrite.graphml import GraphMLWriter
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 4 for calling the TestWriteGraphML obj's underlying member method code with example usage: obj.test_GraphMLWriter_add_graphs() without return types