Google needs to write up a document on this topic.
- We need to write up some A/B testing guidelines.
- Treat Googlebot the same as any other user-group that you deal with in your testing.
- You shouldn't special-case Googlebot on its own, that would be considered cloaking.
- Sometimes it does fall into one bucket (e.g., if you test by locale, or by user-agent hash, or whatnot), that's fine
A/B testing should have a limited lifetime.
- The pages should be equivalent (e.g., you wouldn't have "A" be an insurance affiliate, and the "B" a cartoon series.
- If you have separate URLs, make sure to set the canonical to your primary URLs.
- Googlebot doesn't store & replay cookies, so make sure you have a fallback for users without cookies.