The capability exists to develop and test Trading Systems and Indicators that will work on a several Instruments simultaneously. You can add some symbols onto the same chart and add an Indicator or Trading System  that will use secondary symbols.

To do this you need to add one more instrument to your Tester, by clicking the Instruments... button in the top left corner and then Click Add new: Instrument to handle quotes from both of them. Every time a quote is received you can use direct variables (Symbol, Bid, Ask, etc.) to reach information about Instrument this quote concerns.

To activate one of the existing instrument click on them or right-click and press Activate. Also you may Change symbol name, Remove and edit instrument Settings.

In your scripts OnQuote() function will receive quotes from all symbols on the chart. The first came quote with lesser date/time.

Note: You need to specify the name of the symbol in your trading functions.