A brief introduction to test doubles and mocking frameworks

Unit testing goals

Verification Feedback Speed Focus Isolation

Test Doubles

4 types of test doubleDummy – We just pass it round and don’t do

anything with itFake – Working implementations but take

shortcutsStubs – Canned answers to expected callsMocks – Pre programmed with responses

and expectations that certain calls should be made

Why? Feedback cycle needs to be as small as

possible to be useful We need to remove pain points from

being necessaryDatabase callsUIThird party libraries

We can remove reliance on the rest of the code being complete before knowing the current unit works

Mocking frameworks

Provide a repeatable way to set up mocks/stubs/fakes with little code cost.

Test logic can stay within test We can develop as we test and get

immediate results (TDD)

Rhino.Mocks One of the most mature and feature

complete mocking frameworks Uses castle remoting to mock calls

Not able to mock static or sealed calls Fast Record/Replay Syntax Lots of help and code examples

available Open Source

Typemock Isolator

Mature and fully featured Uses IL Generation

Can mock static classes and callsCan chain events

Commercial licence available for full feature set and support

Main commercial mocking framework so features ++

Moq

New Kid on the block .net 3.5 only No record/replay semantics, just

expectations Less code clutter to tests Not feature complete In active development Open source

How?

It’s time to code

Links

Rhino Mocks: http://www.ayende.com/projects/rhino-mocks.aspx

Typemock: http://www.typemock.com/ Moq: http://code.google.com/p/moq Me: http://www.bgeek.net

owen@bgeek.nethttp://www.twitter.com/buildmaster