If you're developing a Mac application as a universal binary on an Intel platform, then a quick way to test whether it runs on PowerPC/PPC is by forcing it to launch with Rosetta.

Here's how:

1. Select your application icon
2. Click "File" -> "Get Info"
3. Tick the "Open using Rosetta" tickbox
4. Close the info dialog
5. Launch your application

This is a quick and dirty way to test a universal binary, especially useful if you're on a tight budget. However, ultimately the only way to be 100% certain your universal binary runs on a specific platform is to run it on that platform.

Tip: you can also launch Rosetta from the command-line with the translate command. For example this is how we test iArchiver on our Intels:

  $ /usr/libexec/oah/translate \
     /Applications/iArchiver.app/Contents/MacOS/iArchiver