def testKeyCanBeAssignedOnlyOne(self):
     key = "key"
     string = String(key, [])
     self.assertEqual(string.key, key)
     try:
         string.key = "different key"
         self.fail("This operation should fail")
     except AttributeError:
         pass
 def testKeyCanBeAssignedOnlyOne(self):
     key = "key"
     string = String(key, [])
     self.assertEqual(string.key, key)
     try:
         string.key = "different key"
         self.fail("This operation should fail")
     except AttributeError:
         pass