Answer by Lev for What's the difference between a mock & stub?

Here's a description of each one followed by with real world sample.

• Dummy - just bogus values to satisfy the API.

Example: If you're testing a method of a class which requires many mandatory parameters in a constructor which have no effect on your test, then you may create dummy objects for the purpose of creating new instances of a class.

• Fake - create a test implementation of a class which may have a dependency on some external infrastructure. (It's good practice that your unit test does NOT actually interact with external infrastructure.)

Example: Create fake implementation for accessing a database, replace it with in-memory collection.

• Stub - override methods to return hard-coded values, also referred to as state-based.

Example: Your test class depends on a method Calculate() taking 5 minutes to complete. Rather than wait for 5 minutes you can replace its real implementation with stub that returns hard-coded values; taking only a small fraction of the time.

• Mock - very similar to Stub but interaction-based rather than state-based. This means you don't expect from Mock to return some value, but to assume that specific order of method calls are made.

Example: You're testing a user registration class. After calling Save, it should call SendConfirmationEmail.

Stubs and Mocks are actually sub types of Mock, both swap real implementation with test implementation, but for different, specific reasons.