I've been refactoring some tests and changed them from using a global set of users/roles defined as fixtures to instead be factories.
OK, for java folks I'm going to give you the secret ruby decoder ring.
Fixtures = predefined data that you create by manually seeding via seed.rb
Factories = data generated via a factory method at runtime
It's interesting that the ruby community has decided to overload the meaning of these terms to be very specific. I say this because in the "rest of the world" when dealing with testing, a test fixture is a much more generic concept. Typically it is the thing that sets up the test and tears down the test. Yes, often it creates data, but that is not necessarily it's job.
Factories = This is a term that alludes to a well known and fundamental design pattern that can be used for a million different things and honestly has fallen out of vogue with java folks in favor of using dependency injection instead. It seems many folks think that using a factory to generate data for a test case has some inherent advantage over using pre-seeded global data (or other patterns). The primary advantage stated is that it moves the generation of the data closer to the thing being tested.
This is a very good reason, but it doesn't actually eliminate fixtures (generally speaking), it simply moves the fixture from a global scope into a more specific scope. The obvious downside to this is that for things that recur in multiple scopes, you are now repeating yourself.