Backtesting mtgox for historical trade analysis?
bitcoincharts.com will let you download their entire trade history of any exchange (for free) here: http://api.bitcoincharts.com/v1/csv/. Given the raw trade data (amount, price, timestamp), with some code, you can construct candles. I'm not sure this is of any use, though, because I don't know what kind of backtesting you're doing and whether you are dependent on some existing software that may or may not work with raw trade data (or whether you can make candles from it).