无法替换方法的结果。的Mockito

Question

有一个名为SessionManagerTest的类。在其中，我按照原样进行模拟，并尝试替换getCurrentSession方法的结果。

private SessionManager sessionManager;
@Before
public void init () {
    sessionManager = Mockito.mock (SessionManager.class);
    Mockito.when (sessionManager.getCurrentSession (any(), anyInt())). ThenReturn (new MyClassSession (1, 20171111, "cash_user"));
}

方法本身，来自SessionManager类

public MyClassSessionI getCurrentSession (BridgeConfigI bridgeConfig, Integer sessionDay) throws MyException {
    MyClassSessionI myClassSession = getSessionFromCache (bridgeConfig.getMandatoryParam ("user"), sessionDay);
    if (Optional.ofNullable (myClassSession) .isPresent ()) {
        sessionValidator.check (myClassSession);
        return myClassSession;
    }
    myClassSession = getSessionFromDatabase (bridgeConfig, sessionDay);
    if (Optional.ofNullable (myClassSession) .isPresent ()) {
        sessionValidator.check (vinnicaSession);
        addSessionToCache (myClassSession);
    }
    return myClassSession;
}

但结果不是替代品。并执行getCurrentSession方法。我不明白为什么会这样呢