Back in 2007, developer FluBBa created a program that runs on original Sega hardware and tests the SMS mode of the VDP chip. Now, enik2 has updated the VDP test program to run properly on SMS, Genesis and both versions of a Game Gear as well!
Simply load the compiled ROM onto a ROM cart, or single flash cart and run it on your Game Gear. You’ll need to select the right test software to match your Game Gear version (1 ASIC or 2 ASIC), then just let the test run. Please note that running the wrong version of the test, or running it on emulation will result in the errors shown in the screenshot above.
I imagine this software will be useful in getting software emulation more compatible with original hardware, as well as just simply testing Game Gears to see if their VDP’s are working properly!