DeSmuME

The DeSmuME emulator is a Nintendo DS emulator which runs on a computer.  It might seem odd to install a DS emulator on a PC if you've already got a DS Lite and a Homebrew card.  I've used DeSmuME for:

• Using my computer to validate a ROM I backed up NDS Backup Tool works before copying to my SD card.
• Checking that a ROM I patched to play on WIIMMFI still launches before copying to SD.

On the web:

http://desmume.org/
https://en.wikipedia.org/wiki/DeSmuME