You can either check the Last Scanned File field for the Outlook/Exchange provider (accessible by double-clicking the avast tray icon) or send yourself the EICAR test file.

It’s a special file that all AVs detect as virus but is really not a virus - it’s just a test file to test that an AV is working.

http://www.eicar.org/download/eicar.com

Vlk