Can a search robot index a resource that was not pointed to anywhere?

Question

Search Engine Optimization

Good afternoon!
Hypothetical situation: there are two subdomains, one main, and the other, for example, for testing. Both are open for indexing, but there is not a single link to the test domain anywhere. Actually the question is: can a search robot find this second domain and index it, despite the lack of links?

Answer 1

Without links, the subdomain cannot be indexed. But just in case, put robots.txt with a ban in the root of the subdomain. Suddenly the same flashes where the link.

Answer 2

Yes, maybe if you send a link to a friend via messenger. Skype, Hangout, ICQ all merge.

Answer 3

well, you somehow go to the test site and others go in,
and if the metric is worth it, it will say that the site has a
bunch of extensions in the browser, it signals to search engines that there is a site
if you want to close it, then do password authorization
robots is also a solution, but some bots ignore it