Test doubleEdit

Created , updated

A test double is an object which stands in for a real object during automated testing.

Types of test doubles include:

  • mocks: for verifying expectations about messages sent (or not sent) to an object; they do this by intercepting messages, checking parameters, and optionally returning specified values or otherwise inserting behavior (such as raising exceptions)
  • stubs: for intercepting messages, checking parameters and optionally returning specified values or otherwise inserting behavior; in other words, these are just like mocks but without the verification component
  • proxies: special variants of either mocks or stubs, they can be used to verify, intercept or insert, but also invoke the corresponding method on the real object
  • spies: another special variant, again like a mock or a stub, but offering the possibility of retrospectively asking the double if it received a specified message or not

Ruby test doubles

My favorite test double library right now is RR, due to its compact, elegant syntax and wide range of doubles, including proxies and spies. RSpec also comes with a solid mocking framework.