code: def test_simple_graph():
      elist = [(0, 1), (0, 2), (1, 2), (0, 1)]
      g = dgl.graph(elist)
      assert g.is_multigraph
      sg = dgl.to_simple(g)
      assert not sg.is_multigraph
      assert sg.num_edges() == 3
      src, dst = sg.edges()
      eset = set(zip(list(F.asnumpy(src)), list(F.asnumpy(dst))))
      assert eset == set(elist)
  
imports: import math
  import os
  import unittest
  import backend
  import dgl
  import dgl.function
  import dgl.partition
  import networkx
  import numpy
  import pytest
  from scipy import sparse
  from utils import parametrize_idtype
  from utils.graph_cases import get_cases
label_desc: Use image node_id 11 for calling a global function with example usage: test_simple_graph() without return types