Why should I use RSpec or shoulda with Rails?

I personally prefer Shoulda to RSpec. I find that Shoulda has less magic syntax than RSpec. My problem with RSpec is that yeah it's very readable when I read it aloud, but when I get to writing it, hmmmm, I'm never sure how a given assertion should be written. Prag Dave explains the problem better than me. He also likes Shoulda and has a few examples.

RSpec and similar frameworks are tooling designed to aid in Behavior Driven Development. They're not just a prettier way to write tests, though they do help with that.

There is plenty of information on BDD here: http://behaviour-driven.org/And wikipedia: http://en.wikipedia.org/wiki/Behavior_Driven_Development

There are too many benefits to list here, so I'd recommend browsing that site a little.

There are two different things here:

The first thing is what framework to use for writing tests/specs. Here you can choose between Test::Unit, RSpec, Shoulda and so on. The choice is whether you want to do traditional TDD (Test::Unit) or whether you prefer the alternative ways of thinking about specifiying behaviour advocated by developers like David Chemlinsky (RSpec and to some extent Shoulda).

The second thing is how to handle test data. There are Rails fixtures and alternatives desgined with other goals such as the FixtureReplacement plugin. Before Rails 2.0 fixtures had significant and well-documented pratical problems. Many of the practical issues were fixed in Rails 2.0. However fixtures can lead to inadvertent test coupling and some of the alternatives try to avoid this.