improving design through test driven development (tdd)

Improving Design through Test Driven Development (TDD)

Sam Brown @SamuelBrownIVMike McGarr @jmichaelmcgarr

DC Agile Engineering Conference#DCAEC12

About Us

Sam Brown• 11 years software engineer• DevOps Evangelist at Excella• Certified Scrum Master• Puppet Certified

Professional

Mike McGarr• 11 years software engineer• Directory of DevOps for

Blackboard Learn• Founder of the DC

Continuous Integration, Delivery and Deployment Meetup

Types of Tests

Unit Tests

Fast

Independent

Repeatable

Self-Verifying

Timely

Test Driven Development

http://reddevnews.com/articles/2007/11/01/testdriven-development-tdd.aspx

Golden Rule of TDD:Never write production code without a failing test

TDD improves quality

http://www.manning.com/koskela2/

anddesign

Coupling

Cohesion

Object Oriented Design Principles

Single responsibility principle (SRP)

Open/close principle (OCP)

Liskov substitution principle (LSP)

Interface segregation principle (ISP)

Dependency inversion principle (DSP)

Bowling Game• Ten Frames per game• 2 rolls per frame• Unless a strike is rolled

• Properly calculate Spares• Properly calculate Strikes

http://playcasper.com/venues/show/17

Design Decision

Design Decision

Notice the duplication in the tests. Let’s

refactor this.

More duplication

Design Problem – roll() calculates score

Let’s Refactor!

We need a concept of frames.

Ugly Code

Design Decisions

• Design client interface

• Refactor• Change design without changing behavior

• Defer to last responsible moment• Avoids “Big Upfront Design”

New Requirements!

Requested Changes

The Bowling game is becoming service oriented!

• New Requirement:– Post rolls in real-time

Collaborator

Test Doubles

• Dummy• Stubs• Fake• Mocks• Spy

NullPointerException!We need a default implementation.

Contact Us

• J. Michael McGarr• jmcgarr@gmail.com• @jmichaelmcgarr• http://earlyandoften.wordpress.com• DC CI Meetup - http://bit.ly/YRnrwx

Sam Brownsamuel.brown@excella.com@SamuelBrownIVhttps://github.com/samueltbrown

Cute Baby Arrival 12/20/2012