There is no GTA V beta test. Let us repeat that: there is no GTA V beta test. There wasn't one back in March, and there isn't one now.
However, even so, some users have reported seeing links, ads, and banners inviting them to sign up for a purported GTA V beta. If you see such an invitation, do not click it. Above all, do not download anything related to a supposed beta. It will be a scam and possibly infect your computer with viruses.
Rockstar has even go so far as to release an official warning about fake beta scams, after a supposed PC beta "leak" tricked players into trying to join.
We're sure many of you know to be wary of random betas that were never announced, but we also know that people don't always think clearly when they're excited about something. If there ever is a real GTA V beta, Rockstar will announce it and we will let you know.
Also, just so you know, Rockstar has never had a beta for any Grand Theft Auto game, and that trend does not look like it's about to change.