docs: def return_value(self):
          """
          Returns the value for this expectation or raises the proper exception.
          """
          if self._raises:
              # Handle exceptions
              if inspect.isclass(self._raises):
                  raise self._raises()
              else:
                  raise self._raises
          else:
              if isinstance(self._returns, tuple):
                  return tuple([x.value if isinstance(x, Variable)
                               else x for x in self._returns])
              return self._returns.value if isinstance(self._returns, Variable) \
                  else self._returns