I dont agree..even if backtest is not 100% reliable it gives you a good idea on how the expert would behave in difficult situations. Then you can analyze the worst case one by one and check whether the trades shown by the backtest were indeed taken following the rules of your expert...

If there is no backtest, then forward test during 2 or 3 years may be necessary to cover all type of markets, and be sure that the experts covers them all.

Especially the PID is working fine during ranging market, but what would happen in case of very strong trending market without any retracement, as we had for euro sooner this year?