Test-driven development inwith BabyMock 2

Attila MagyarFOSDEM 01/02/2014Brussels

Who am I?

Attila Magyar

● Java for living● Smalltalk for joy, since 2012

● Python, Groovy, Lisp, etc..

● TDD for about 4 years

Contact: http://twitter.com/zeroflag

Agenda

● About TDD and Mock objects in general

● About BabyMock 2● Differences between the new and the old version● How does it work?● Few words about the internals

● DEMO

Outside-in TDD with Mocks

A

B

C

Message 3

Message 4

Message 1

Response

Test Message 2

Outside-in TDD with Mocks

A

MOCK B

MOCK C

Message 3

Message 4

Message 1

Response

Test Message 2

●Expect Message 3● Exactly once● With x argument

●Allow Message 4● Any number of times● With y argument● Answer „Response”

Inter-object protocol

● Get a good mental picture of the objects relationships, and the inter-object protocol

● Identifying test failures is easier

BabyMock is a visual mock object libraryhttp://smalltalkhub.com/#!/~zeroflag/BabyMock2/

The old syntax (BabyMock 1)

The new syntax (BabyMock 2)

ExpectationsUnder the hood

How does it work?

● Mock object is a Proxy that intercepts all messages

● Using the doesNotUnderstand is easiest way to implement it (but limited).

● Nil methodDictionary + cannotInterpretMore information: Efficient Proxies in Smalltalk by Mariano Martinez Peck et al.

BabyMock visualized with BabyMock

BabyMock visualized with BabyMock

BabyMock visualized with BabyMock

DEMO

ShoppingCart

● CreditCard

● PriceCatalog

● Adding new item ids

● Paying for its content

Food for thought

● http://jmock.org/ (https://github.com/jmock-developers/jmock-library)

● Evolving an Embedded Domain-Specific Language in Java, Freeman, S. and Pryce, N.

● Mock Roles, Not Objects. OOPSLA 2004, Freeman, S., Mackinnon, T., Pryce, N., Walnes, J.,

● Growing Object-Oriented Software, Guided by Tests, Freeman, S. and Pryce, N.

● Efficient Proxies in Smalltalk, Mariano Martinez Peck et al.