You can make your own simulator. With some finagling, it is possible to get the code from your robot to comile on a PC. You can then feed the program inputs and print out the outputs to see if they match what you want. If you want to get fancy, you can make your own GUI to simulate your whole OI and display outputs. This is what I have done so I can (theoretically) test all code before placing it on the robot and have confidence that it works.
Here is a pic:
