Google has issued an update to how developers use the Play Store to test apps. There aren't as many options, but the entire setup is simpler. You've got internal tests, closed alpha, and open beta. That's it.
Previously, you could create an open alpha or closed beta test, but no more. Developers won't lose access to such tests, but they cannot create more. According to Google, internal tests are intended for a small group in the dev team. An alpha release will always be closed going forward, so you have to manage a list of users. Betas will always be open, so users can visit the landing page to join.
This approach makes more sense on the user side, so you don't have to guess how a developer is going to run a beta or alpha. There's just the one version of each.
- Google Support