new_contents: import unittest
  
  from lib import client, response
  
  
  class TestAccountEndpoint(unittest.TestCase):
  
      def setUp(self):
          self.client = client.Client()
  
      def test_get_single_balance(self):
          expected_response = {u'status': u'1', u'message': u'OK', u'result': u'748997604382925139479303'}
          address = '0xde0b295669a9fd93d5f28d9ec85e40f4cb697bae'
          result = self.client.get_single_balance(address)
  
          self.assertIsInstance(response.SingleAddressBalanceResponse, result)
          self.assertEqual(expected_response, result.etherscan_response)
          self.assertEqual(200, result.response_status_code)
          self.assertEqual('1', result.status)
          self.assertEqual('OK', result.message)
          self.assertEqual(748997604382925139479303, result.balance)
  
subject: Add tests