Hi, 

let's say I have a page domain.com/page-1 

Now I create two variations  domain.com/page-1a and  domain.com/page-1b

and create an URL split test.

How do you prevent page-1a and page1-b being from being indexed.

What's the best approach:

Add a noindex on those pages?

Or using canonicals to link to the original page?

What do you recommend or is anything already happening automatically?