code: def test_dynamic_getitem(self):
      def fn(a, b):
          return a[b.size(0) - 1]
  
      cnt = torch._dynamo.testing.CompileCounter()
      opt_fn = torch._dynamo.optimize(cnt)(fn)
      for i in range(3, 12):
          opt_fn(torch.randn(i), torch.randn(i))
      # just one graph
      self.assertEqual(cnt.frame_count, 1)
  
imports: from unittest.mock import patch
  import torch
  import torch._dynamo.test_case
  import torch._dynamo.testing
  from torch._dynamo.testing import unsupported
  from torch._dynamo.utils import ifdynstaticdefault
label_desc: Use image node_id 31 for calling the SubGraphTests obj's underlying member method code with example usage: obj.test_dynamic_getitem() and returns: a