It would be cool to easily adjust the timeframe in which the backtest should test. A Stategy can work in bull markets very good and can blast your account then an bear market. In these times it would be very helpful to test only the bear market conditions. By giving a start and an end date it would be possible to tests the stategy only in the critical times.
The code is already written in the link below and has just to be added to your stategies.