code: def testIndexing(self):
      n = self.g.vcount()
      for i in range(n):
          self.assertEqual(i, self.g.vs[i].index)
          self.assertEqual(n - i - 1, self.g.vs[-i - 1].index)
      self.assertRaises(IndexError, self.g.vs.__getitem__, n)
      self.assertRaises(IndexError, self.g.vs.__getitem__, -n - 1)
      self.assertRaises(TypeError, self.g.vs.__getitem__, 1.5)
  
imports: import unittest
  from igraph import Graph, Vertex, VertexSeq
  from .utils import is_pypy
label_desc: Use image node_id 3 for calling the VertexSeqTests obj's underlying member method code with example usage: obj.testIndexing() without return types