First you may use backtesting. Here you take your system and work out on paper how well it would have done on the recent historic market, i.e. The last six months or whatever period you select. Backtesting should give you an idea of whether a system has potential. Naturally the market is not going to copy in exactly the same way so you do need to take into account the proven fact that you may have struck fortunate or unlucky and picked a point when the system performed surprisingly well or badly.
This is explained well by considering http://www.forexmachines.com/reviews/unstoppable-forex-profit/. The second way to check forex systems is in a demo account. This technique is slower because you have got to wait for your signals to come up in reality. On the other hand, it emulates real live trading methods with the possibility of slippage and other factors which aren’t gong to show up in back testing. Remember that you can test many systems at the same time in a demo account, provided you keep separate records of their performance. In this way you’ve got a better chance of ending up with one moneymaking system at the end of your period of testing. This gives you solid real time coaching to prepare you at present when you go live with real money. Most forex brokers will provide free demo accounts which you may use to check forex systems.