http://www.amazon.com/Eloquent-Ruby-Addison-Wesley-Professional-Series/dp/0321584104
book-eloquent-ruby#mock-definition1 "A mock is a stub with an attitude. Along with knowing what canned responses to return, a mock also knows which method should be called and with what arguments. Critically, a disappointed mock will fail the test. Thus, while a stub is there purely to get the test to work, a mock is an active participant in the test, watching how it is treated and failing the test if it doesn't like what it sees." book-eloquent-ruby#mock-definition1