Everyone can help testing by playing beta games and posting replays and feedback.
You can always find the latest patchnotes here: http://content.faforever.com/patchnotes/index.html
How to make a good feedback report:
-Post in the appropriate thread, or create one if it doesn't exist
-Post your replay
-Give some basic information about your game(s): Rating range, map, number of players, any special gamemodes/options
-Give a short description of when and what is happening in the game that concerns changed units
-State your opinion if you like or dislike the change and why
Example:
Janus: ~1800 teamgame on open wonder
Description: Janus rush on wonder starting at minute 4, janus do great damage to t1 pgs but die quickly to inties. Continuous janus use from several players throughout the game with various success.
Opinion: Janus bombs look incredible cool now and the unit seems to be strong if used well but also counterable with decent effort. Changes are good.