The alpha testing will come when they’re ready to release it. In the meantime, you can pass the time by playing the pre-alpha version which has been out for 20 years. 
If you have the original game and haven’t yet bound your codes to your Blizzard account, you can do so by going to your Blizzard account overview and entering the game keys from the box into the “Redeem a code” field.
If you don’t have the original game and want to play NOW!!11, you can pick up the game+LoD expansion for $20.
Under “Classic Games”.
If you do decide to play the original game, I highly recommend using Sven’s Glide Wrapper. I’ve posted a setup guide to aid in getting it working.
Also if you do play the original game, if you use a VPN service, be sure to turn it OFF when playing on Battle.net! Also public/business connections are not allowed. (Either will cause a two-week restriction from Battle.net access in Diablo 2)
This is my experience of Bizzard’s “soon”.
Remember when I heart above D2 1.10 patch would be released “soon” years ago, I started to warm up with patch 1.09 during the time for waiting the new patch. And that warm up took me 1 year.
So, if I can see D2:R Alpha within 6 months, I will call it “suddenly” in stead of “soon” LOL.
They memed themself too with the 1.10 patch. Hell hath frozen over, the 1.10 patch is here! or something to that degree I remember.
They’re busy adding personal loot for testing.
If that so I would say a huge sarcastic THANK YOU to those who asked for it.
Blizzard has officially acknowledged the term “Blizzard soon” as not soon.
I hope Blizzard / Vicarious Visions doesn’t touch the loot system.
Lol. I can see the alpha coming sometime next month. Let’s not rush them. I want the game to be as perfect as possible.
Yes I agree, I guess sometime in April.
I’m hoping for my prediction is right, single alpha during the D3 season lull, starting around 3.28, multi a month or so later, then launch on June 29th, I kinda wanna say June 28th as it’s in the middle of D2/Lod releases.
If they miss the anniversary it will be a lost opportunity.
People moaning about graphic assets are going to get the alpha delayed because well because. There’s no good reason for this.
Whats the point of releasing it when it doesnt have proper graphic remaster? Thats whole point of remaster.