It is likely that this was a spam since you are already a diamond member and there are no "free membership trials" for beta testing etc, and I'm sure chess.com doesn't send membership trials in doc files.
What was the exact e-mail address that you received the e-mail from?
Hi,
I receive a email from chess.com who offer me a free membership trial to try new improvements on the web site.
Links dosn't seems to work and bring me on a google docs form.
No sign of this promo on the web site. Is this a spam?
Thanks for your help.
rl