Mocha comes in three parts:
Mocha and Stubba have been created by amalgamating a number of techniques developed by me and my Reevoo colleagues (Ben, Chris and Paul) 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.