Now there is no single way to do this, so we can only provide a general guideline here. This example assumes you want to do A/B testing for marketing purposes, and that your users have been semented into groups a and b.

1.  Create different folders with the same files for A/B - let's say /round1a/ and /round1b/
2. In each folder, create the same files - for example /round1a/_cta.cshtml and /round1b/_cta.cshtml. Customize these to your needs, till they do what you want. 
3. Now in the root folder, create the gateway razor file - /_cta.cshtml. In here, you'll check for what group the user is in, and then simply do a @RenderPage(groupName + "/_cta.cshtml")