Mocha is a Ruby mocking library with a syntax like that of JMock and
SchMock, but with a couple of useful extras. It comes in three parts:

  Mocha - traditional mock objects with expectations and verification
  Stubba - allows mocking and stubbing of methods on real (non-mock)
classes and instances
  AutoMocha - magically provides mocks in the place of undefined classes

RDoc - http://mocha.rubyforge.org
Download - http://rubyforge.org/projects/mocha

Mocha and Stubba have been created by amalgamating a number of
techniques developed by me and my Reevoo colleagues (Ben Griffiths,
Chris Roos and Paul Battley) into a common syntax. Both Mocha and
Stubba are in use on real-world Rails projects.

AutoMocha is more experimental and is at an earlier stage of
development. It's an attempt to make it easier to write true unit
tests (i.e. tests with no external dependencies).

You can find examples in the RDoc README and in the acceptance tests.

James
http://blog.floehopper.org