Backtesting

Does anyone know of a good tool that I can use to backtest different portfolios as much as possible without having to make it myself? The top Google results are all extremely limited. Especially if you try to bring in German withholding tax or trend rules (e.g. “sell at sma200”). I don't want TA fanfiction, very simple rules are enough. Or is that fundamentally wrong because a portfolio whose success depends on a 26% cap tax is of no use anyway? Thanks! submit