Test Driven Development
In An Agile Environment
Presented by Mr. Viraf Karai
on Mon. Jan 19, 2009

Topics covered
Agile manifesto Myths about TDD
 
Evolutionary dvlp & TDD benefits
 
design Ideal qualities of unit

TDD philosophy tests

TDD steps Resources
 
TDD states

Legacy development

2

The Agile Manifesto
Composed by heavy hitters in the software industry

in Snowbird, UT in February 2001
Included folks backing methodologies such as

Scrum, XP, Crystal, Feature driven developemt, etc.
Big names such as Martin Fowler, Robert C Martin

(Uncle Bob), Alistair Cockburn, Ken Schwaber,
Dave Thomas, etc.
3

The Agile Manifesto – principles
Primary metric of progress is
Continuous delivery 

working software
Welcome changing reqs

All participants should

Deliver working software

maintain a constant pace
frequently
Continuous attention to tech

Involve biz and developers

excellence & good design
throughout the project
Simplicity is essential

Build projects around

Self organizing teams
motivated folks 
Periodic retrospectives
Communication should be 

face­to­face
4

A couple of quotes
The act of writing a unit test is more an act of design
than verification (Robert C Martin aka Uncle Bob)
Walking on water and developing software from a
specification are both easy if both are frozen
(Edward V. Berard)
5

Evolutionary dvlp and design
Evolutionary development is an iterative and incremental approach
to software development.
Instead of creating a comprehensive artifact, such as a requirements

specification, that you review and accept before creating a
comprehensive design model (and so on) you instead evolve the
critical development artifacts over time in an iterative manner.
Instead of building and then delivering your system in a single “big

bang” release you instead deliver it incrementally over time. Yes, you
will likely still need to do some initial requirements and architecture
envisioning, but this is at a high level ­­ I can't say this enough, you
don't need to do big modeling up­front (BMUF)
– Scott Ambler
6

Evolutionary design steps
7

Test Driven Dvlp (TDD) Philosophy
The basic tenets are developing and implementing

unit tests before writing a line of code
Unit tests will and must fail up front

Code is developed after the test is developed.

A unique idea that is still foreign to many

developers
8

TDD steps
9

TDD steps
Quickly add a test ­ just enough code to fail test

Run test­suite to ensure test fails (may choose to run

a subset of suite)
Update your functional code to ensure new test

passes
Re­run test suite and keep updating functional code

until test passes
Refactor and move on

10

TDD states
11

TDD and agile
TDD implies agile.

Strong emphasis on testing

Tests should span entire breadth of codebase

Once all software is ready for delivery, all tests

should pass
A unique way to address modern challenges in

software development
12

Legacy software dvlp and testing
Mostly implies a waterfall/big­bang process

Very little emphasis on unit testing by developers

Tests are almost developed as an afterthought

Tests are mostly manual

Huge emphasis on QA team

Delivering quality software on time and within

budget is almost accidental
13

Myths about TDD
Myth: TDD is ok for small projects involving a

handful of folks but won't scale to large projects
involving scores or hundreds of people.
Answer: Not true.

Kent Beck worked on a pure TDD project developed in

Smalltalk.
4 years and 40 man years of effort resulting in 250K lines

of func code and 250K lines of test code
4,000 tests run in under 20 mins

Full suite runs several times a day

14

TDD benefits
Shortens the programming feedback

Provides detailed (executable) specifications

Promotes development of high­quality code

Provides concrete evidence that your code works

Requires developers to prove it with code

Provides finely­grained, concrete feedback (in mins)

Ensures that your design is clean by focusing on creation of

operations that are callable and testable
Supports evolutionary development

15

Six ideal qualities of unit tests
Decisive – has all info to determine success/failure

Valid – produces a result that matches the intention of the work

artifact under test
Complete ­ contains all the information it needs to run correctly with

a given test harness and work artifact under test
Repeatable ­ always gives the same results if the test harness and the

artifact under test are the same i.e. Is deterministic
Isolated ­ is not affected by other tests run before it nor does a test

affect the results of tests run after it
Automated ­ requires only a start signal in order to run to completion

in a finite amount of time
16

Why TDD
If it's worth building, it's worth testing.
If it's not worth testing, why are you
wasting your time working on it?
­ Scott Ambler
17

Resources
Test Driven Development By Example – Kent Beck

Test Driven: TDD And Acceptance TDD For Java

Developers ­ Lasse Koskela
http://www.testdriven.com

http://www.agiledata.org

Junit 4 in 10 minutes

http://www.instrumentalservices.com/media/articles/java
18

Questions
19