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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_expectation(self, caller):
 """Adds a new expectation for the method. :return: The new ``Expectation``. :rtype: Expectation """


        expectation = Expectation(self._target, self._method_name, caller)
        self._expectations.insert(0, expectation)
        return expectation