Here’s everything I could find out about testers in stuff published by Infocom.
Game manuals refer to several Imps as former testers: Steve Meretzky, Jeff O’Neill, “Hollywood” Dave Anderson, and Amy Briggs.
The Wishbringer InvisiClues credit the following testers: “Hollywood” Dave Anderson, Joanne Avtges, Gary Brennan, Amy Briggs, Mark “Max” Buxton, Liz Cyr-Jones, Suzanne Frank, and Jeff O’Neill, “plus dozens of beta- and gamma-testers too numerous to list.”
If you pull up the credits in Trinity, using either of the commands ASK WOMAN ABOUT TRINITY or $CREDITS, the first line credits the following under “Testing”: Gary Brennan, Amy Briggs, Suzanne Frank, Max Buxton, and Liz Cyr-Jones.
The Leather Goddesses of Phobos InvisiClues says this under “Acknowledgements”: Testing: The primary testers for Leather Goddesses of Phobos were Tom Bok, Gary Brennan, Amy Briggs, Max Buxton, Liz Cyr-Jones, Suzanne Frank, and Matt Hillman. In addition, dozens of outside testers deserve praise for their help.
The New Zork Times/The Status Line includes quite a few mentions of these testers, including such facts as that Tom Bok was the son of the president of Harvard, and that Gary Brennan had formerly cared for sponges at MIT.
Also, Chip Hayes posted on RGIF back in 2001 that he had been one of the outside testers. He provided patch files for the Gamma versions of Trinity, LGOP, and Hollywood Hijinx, which are in the archive.
There were more than 50 other outside testers, but information on them has not been made public.