Run beta versions of sites SEO safely [duplicate]

We have and want to test a new site template on

What is the correct way to run a beta test without affecting SEO of the main

In the topic SEO safe way to run beta of new site on seperate domain I found 2 recommendations:

  1. Putting a robots.txt with noindex to our
  2. Canonicalizing to – Why? In any case we already have the noindex flag…

Does it still actual in 2020? Do you have any other recommendations?

By the way, do we need to register in Google Webmasters Tools?