Unit test / Test doubles

Test doubles

"Test Double is a generic term for any case where you replace a production object for testing purposes" - Martin Fowler

• Dummy
• What does it do?
• It does almost nothing. You just need it (for example) to pass as a parameter to a constructor.
• Example?
• A dummy class has a method which returns null.
• Stub
• What does it do?
• Kind of dummy. It does a thing. It returns a specific value.
• Example?
• A stub class has a method which returns true.
• Spy
• What does it do?
• Kind of stub. Saves any kind of things what you might need to check at the end of your test.
• Example? 
• A spy class saves whether its "foobar" method has been called.
• Mock
• What does it do?
• Kind of spy. Does behavioural testing. It knows what behaviour is expected. What function was called, with what arguments, when and how many times.
• Example?
• A mock expects the "validate" method will run 2 times and will return true.
• Fake
• What does it do?
• Business behavioural testing. It can return different values based on different parameters.
•  Example?
• A fake class has a method which returns true if the logged in user's name (a parameter) is "root" else returns false.

 

It is beneficial to read uncle Bob's article.

References
http://blog.8thlight.com/uncle-bob/2014/05/14/TheLittleMocker.html