code: def test_len(self):
      BasicTestMappingProtocol.test_len(self)
      d = self._full_mapping({"a": 1, "b": 2})
      self.assertEqual(len(d), 2)
  
imports: import unittest
  import collections
  from test.support import Py_C_RECURSION_LIMIT
label_desc: Use image node_id 7 for calling the TestMappingProtocol obj's underlying member method code with example usage: obj.test_len() without return types