as mr. Pisa stated, it is perfectly possible to log in to two instances of tws and use different port numbers to send signals to a live or simulated account.
regarding testing, the best thing you can do is to use out of sample data. if you have 10 years of data, leave the last 2 out of sample and when you then add this data you will have an excellent evaluation of how your systems would have performed in real time, live data.
also, ninjatrader is the best platform i know and it is free to use on simulator to evaluate all kind of strategies, i recommend it.
