How do I make a performance test?

Hi.

I would like to make a performance test using rails 2.3.3

I see there is a generator called performance_test, but can someone
give me a link to a url that gives some examples.

I have read
http://guides.rubyonrails.org/performance_testing.html

To me however a test is something that either passes or fails. And all
the examples given in article provides measurements of executions in
numbers. I wouldn't call these tests. I would call that performance
measures. I would like to write a test that passes when a certain
performance measure is below some threshold, and fails otherwise.

Any hints on where to start RTFM?

Jarl