...two major concerns:
- Duplicate Content: the act of copying content from elsewhere and hosting it on your site. Search engines penalize for such stealing of content because you cannot expect to rank on keywords for the content that isn’t yours. Again, many A/B and multivariate testing software (including VWO) have an option where you can redirect site traffic to different variations of a page which raises this concern.
Properly done A/B and multivariate testing do not ruin your SEO investments. I have done numerous tests like that and analytics from search engines never pissed me off afterwards. (Triple knock on the wood though. Never say never. :)