We would like to remove DB access in non-database PHPUnit tests. As a
first step, avoid database usage in tested code when possible. In
particular:
- In NameTableStoreFactory, avoid domain ID normalization if the
provided ID is already false.
- In SpecialDoubleRedirects, do not acquire a DB connection until it's
needed (which is just one place).
- Use editPage() in TitleDefTest instead of a DIY implementation, and
add `@group Database` accordingly.
- Avoid parsing titles in ContentHandler tests that don't need to parse
titles. Among the many dependencies of parsing titles is the interwiki
lookup, which requires DB access.
- Also remove test cases that used the "Gadget" namespace; it doesn't
exist in core, so these pages were actually in the mainspace.
- Mock the database in CategoriesRdfTest. The only two methods that use
the database were already being mocked.
- Add `@group Database` to test classes that are intentionally using the
Database, mainly via getTestUser().
Bug: T155147
Change-Id: I9385fe14cfeb6b7b7378cc322d510034c4ee0711
