These are the notes for GoZync 3. Docs for the latest version of GoZync--GoZync 4--can be found here. GoZync 4 is a free upgrade and is highly recommended (hint: it's faster).
What is Testing Mode?
Testing Mode was introduced in version 3.171
Testing mode reduces the found set of records being considered to pull down to your mobile device. When Testing Mode is ON, GoZync only looks at the last 5 records in each table to see if they've changed since the last sync. This means you can debug big tables much more quickly.
The actual implementation is in the script "Reduce Found Count in Testing Mode"in GoZyncHosted.