docs: def validate_return_value(self, retval):
          '''
          Validate the return value of a function call. If an error occurred,
          the function will throw a TypesafetyError.
  
          The `retval` should contain the return value of the function call.
          '''
  
          if self.__return_annotation is None:
              return
  
          if not self.__is_valid(retval, self.__return_annotation):
              func_name = self.__function.__name__
              msg = self.RET_TYPE_ERROR_MESSAGE.format(
                  func_name,
                  self.__format_expectation(self.__return_annotation),
                  retval.__class__.__name__
              )
              raise TypesafetyError(msg)