what would you do in this situation? "for beta testing"

I would contact the giveaway creator.

It depends on if it is really a beta key that is going to get revoked at some point or if the dev just labeled it a beta key for one reason or another and it is actually permanent (this is common). Keys bought while a game is in early access are often labeled beta even though you keep the game forever.

https://www.steamgifts.com/discussion/elIQn/so-a-won-another-game-yay-me-but-it-was-a-beta-key
https://www.steamgifts.com/discussion/KBCcB/beta-key-should-i-mark-as-received-or-not
https://www.steamgifts.com/discussion/rE2hZ/won-a-full-released-game-but-the-key-said-the-game-is-for-beta-testing
https://www.steamgifts.com/discussion/fC93V/won-a-giveaway-but-received-a-beta-key-is-it-a-bannable-offence

Keys that are made before the game is in the store are labeled with "for beta testing" but are full game keys.
The bad thing are that Beta Keys that get often revoked after the timeframe for the beta test(s) are also labeled as the same.

From my experiences i never won a game with "for beta testing" that weren't a full game.
So i would say "if you don't seen exactly that game in a Beta freebie, at that day or 1-3 days before the GA creation day, then you shouldn't think it is only a Beta key that get later revoked and be happy about the win :o)"

I would do exactly the same as you mentioned - play it asap, then if it gets revoked later, write a support ticket. You win some, you (might) lose some. Fingers crossed it's just the name.

Contact giveaway creator, inform of the beta key.
He/She will either

1. Give you a new key, a proper one hopefully
2. Ask you to delete the giveaway - Which you may or may not agree to, the regs allow for both. If you agree, then that's that. if not, GA creator still have the burden of providing a proper key.
3. Give you an explanation as ''It's marked as BETA but is full game'', hopefully with the added ''you can check developers comment on it [HERE)''
4. Spin you a yarn and try to get away from it all, at which point you mark it as not ''Not Received''.

Here's the thing, by waiting and just hoping it's alright you yourself are in jeopardy of being punished for rule breaking. If you accept the key - click ''Received'' - on anything different than what was advertised you are helping GA creator to commit fraud against the point system, and for that you may receive a temp-ban. Yes; Fraud, even if not intended by either party. So contact GA creator, if answers aren't satisfactory, click the ''Not Received'', or contact a moderator if you are unsure.

It's absolutely not a problem, a lot of key given by developper have this "for beta testing" appelation.
Normally the creator of the giveaway has had the game with the developer in order to make a giveaway and so there is really little chance that the key will ever be revoked.
For the moment mark the key as received and thank the giveaway creator.
You'll contact support if the key is ever deactivated but I don't think you'll need to do that.

And Iris and the giant is a great great game... Enjoy =) =)

I have seen a few on my keys already that tag while those keys were from bundles. I had such keys in the past from Indiegala, Fanatical even from Humble.

After the release, the game developers can request a limited amount of keys if their steam store revenue not high enough, so sometimes they use the prerelease keys beta keys, which they can ask for many, to send to bundle sites as they simply don't have enough after release keys to met the expected sale amount of the bundle.

These are never revoked, if a developer decides to go shady it is no matter what the activation name it is.
This activation name usually for the press game copies they send to YT-ers, now imagine what a 100k+ YT influencer will rage about a game if their game gets revoken, so you, me, and everyone are safe. Exceptions apply, but as I said already if dev is shady, then even other named activations are unsafe.

I wouldn't do anything, just keep the game, as I have done in the past with 2-3 giveaways with that activation in the past. You need to open a ticket only if the game gets removed, which is unlikely. I personally would stop do any giveaway if there would be a big campaign against these keys because any purchased key could have this tag, except A+ game keys.

As other people wrote all keys that are generated before game is released are marked as for beta testing. Even when they give you full game, and will never disappear from library.

You can try to ask creator about source of key. But if you get copy that unlocked full game, and will not automatically expire after x days - you should mark it as received.

In case key is revoked in few weeks or months:

• write to giveaway creator about it - best place to do this is in giveaway comments, that way we will see something is wrong with the key after we open giveaway
• creator may give you new key or ask for permission to delete giveaway - it is up to you if you want to allow support to delete giveaway
• if you don't want giveaway to be deleted / creator does not respond - write ticket in other category with screenshot of revocation message. It will be forwarded to SuperModerator that can change feedback for giveaway.

When you decide to write ticket about feedback change - write about it in the giveaway comments as well. "Hi I had to write ticket to change feedback for this giveaway, as you did not respond to my previous message". It should prompt support member to check relevant ticket before issuing suspension for inactivated win.

Just don't write reports on creator in such situation - support members can't see them (only moderators and moderators+ can), so they will not be aware you had problem with giveaway. Esp if you just write report, and not leave any message in giveaway itself.