How did you "install" Electrum? Did you open the .dmg, then drag the "Electrum" icon into your "Applications" folder?
If you do that, you should see Electrum.app added to the applications folder.
However, I don't seem to be able to make this script work. I just kept getting an error about TextEdit not having permissions to launch the application. Instead I had to open Terminal and use the following command:
/Applications/Electrum.app/Contents/MacOS/Electrum --testnet
I'm not overly familiar with OSX these days... so I might be missing something obvious.