You can follow this thread to be up to date with new releases of test rules.
Sadly there is no way in the products to filter rules by scope at the moment 
For the test tag, its meaning is to highlight that a rule is about testing best practices or testing frameworks (assertions, junit, mocking, etc..). But rules like “Unused method parameters should be removed” should not be tagged as “test” but should still raise issues on test code.
Ideally, almost all Sonar rules should target also test code, as it is still code that will need to be maintained and used by developers, this does not mean that we should tag all rules as “test”, as the tag itself would lose its meaning