Dummy

• dummy objects are passed around but never actually used
• usually, they are just used to fill parameter lists.

Fake

• fake objects actually have working implementations, but usually take some shortcut that makes them not suitable for production
• behaves exactly the same as their real counterparts
• an in-memory/embedded database is a fake of a real database

Stub

• stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what’s programmed in for the test
• can be used for state verification

Spy

• records how they were called for behavior verification
• usually wraps around an existing object
• used for behavior verification

Mock

• are pre-programmed with expectations that form a specification of the calls they are expected to receive
• creates a new object
• used for
• can be used for behavior verification