Mocha is a Ruby library for mocking and stubbing using a syntax
like that of JMock, and SchMock. Most commonly Mocha is used in
conjunction with Test::Unit, but it can be used in other contexts.

One of its main advantages is that it allows you to mock and stub
methods on real (non-mock) classes and instances. You can for
example stub ActiveRecord instance methods like create, save,
destroy and even class methods like find to avoid hitting the
database in unit tests.

Mocha provides a unified, simple and readable syntax for both
traditional mocking and for mocking with real objects.