code: def test_PushbackAdapter():
      it = PushbackAdapter(iter([1, 2, 3, 4]))
      assert it.has_more()
      assert six.advance_iterator(it) == 1
      it.push_back(0)
      assert six.advance_iterator(it) == 0
      assert six.advance_iterator(it) == 2
      assert it.peek() == 3
      it.push_back(10)
      assert it.peek() == 10
      it.push_back(20)
      assert it.peek() == 20
      assert it.has_more()
      assert list(it) == [20, 10, 3, 4]
      assert not it.has_more()
  
imports: import sys
  import numpy
  import six
  from six.moves import cStringIO
  from .compat import optional_dep_ok
label_desc: Use image node_id 12 for calling a global function with example usage: test_PushbackAdapter() without return types