Initial Setup

This setup only needs to be done once. Add a new set of files to your Project using the "+" in the upper right corner of your project on http://build.particle.io. Name them "GarageHardwareReal". This will create both a .cpp file and a .h file. Hit the "x" on the tab for the .h file and remove it (accept the "Are you sure" window").

Open this GarageHardwareReal.cpp and paste the contents into the GarageHardwareReal.cpp. (This has been updated since the studio, so be sure to use this version)

Add a "#if 0" to the top of your GarageHardware.cpp file and a "#endif" at the bottom. Notice the GarageHardwareReal.cpp starts with a "#if 0" when you download it. We will simply change which file has a 1 and which has a 0 to control whether the code runs with your version of the functions or the version that works with the physical model.

When you're developing using simulated hardware:

When you are working using your breadboard, be sure that your GarageHardware.cpp starts with "#if 1" (rather than #if 0") and that GarageHardwareReal.cpp begins with "#if 0".

Checkout Process:

Have your work reviewed by a TA using the simulated environment.
Search your main .ino and verify that it doesn't ever call pinMode(), digitalWrite(), digitalRead(), analogWrite(), analogRead(), or any other I/O other than method of the Serial object, like Serial.println.
Change the files to disable use of your code and enable use of the code for the real hardware: GarageHardwareReal.cpp should start with "#if 1" and GarageHardware.cpp should start with "#if 0"
Reprogram your Photon. Show a TA/Instructor that you have made the required changes and successfully uploaded your code.
Remove your Photon from your test setup. (When you reinstall it later be sure you line it up correctly! Misalignment could do damage to I/O devices)
Work with a TA/Instructor to test your work with a mini garage. Good Luck!