Question: Suppose I have my live site at `www.mywebsite.com`, tracked and managed via Google Webmaster Tools. Then I want to add to the project list a subdomain like `test.mywebsite.com` which I use for testing purposes. Of course that subdomain shouldn't be tracked or indexed by Google, but I would like to use "fetch as Google" feature on it to see how the crawler manages the pages. Can I set up such a test environment without being indexed by Google?

Answer: 
Not had chance to test this, but I think if you add noindex tags to your site then it should still allow your site to be registered with webmaster tools, as it can still see the site's content in order to detect ownership. 

I believe "fetch as google" then returns live results rather than what is already indexed (it wouldn't be very useful if it didn't allow you to check new pages or re-check updated pages), and so temporarily removing the noindex tag when you run it should allow this feature to be used (it may also return some useful information without removing it). 

The fact "fetch as" has a separate "submit" button suggests to me that it will not automatically index pages found via this method, so that should not be a concern.

Adding canonical tags pointing to your main content would provide an additional security measure to stop it accidentally listing.
Google can't provide any information about your website if it's not indexed. 

In other words, you can use Google Webmaster Tools without your website being indexed, but it will be pretty much useless, since will not provide any data.