What exchange rate is used during backtesting?

Hi!

While I'm developing  robot and running backtests I became curious that if I run the robot on EURUSD and my account is in CHF, you need to calculate the exchange rates, for each deal during the backtest, but its only possible if you're downloading tick data for EURUSD and other currency pairs which makes it possible to calculate real exchange rates.

Is my suspicion correct that you're not using real exchange rates for backtest, but a fixed value, like the first available value in the backtest?

This can make the backtests false in terms of balance and equity if 2 or 3 related currency rates has been changed a significant amount in real world during the test period.

Thanks,

Attila