text: from collections import ChainMap
  from unittest import TestCase
  
  import jsons
  
  
  class TestChainMap(TestCase):
      def test_dump_chain_map(self):
          d1 = {
              'a': 'A',
              'b': 'B'
          }
          d2 = {
              'c': 'C',
              'd': 'D'
          }
          m = ChainMap(d1, d2)
  
          dumped = jsons.dump(m)
          self.assertDictEqual({**d1, **d2}, dumped)
  
      def test_load_chain_map(self):
          d = {
              'a': 'A',
              'b': 'B'
          }
  
          m = jsons.load(d, ChainMap)
          self.assertEqual(ChainMap(d), m)
  