Brandon Byars

bbyars@thoughtworks.com

TEST-DRIVEN DEVELOPMENTBEHAVIOR-DRIVEN DEVELOPMENT

As a software development organization,

I want to have more predictability and adaptability

So that I can respond to change

Given a new requirementWhen I write the code for itThen I want to know whether I did the right thing

Validate

Analyze

Design

Code

Test

Time

Prod

uctiv

ityWHY TDD?

Immature practices

Our goal

dS−− ≥ 0dt

Entropy: It’s the law

Validate

Analyze

Design

Code

Test

ValidateAnalyze Design Code Test

ValidateAnalyze Design

Code

Test

INSIGHT #1: AUTOMATE TEST VERIFICATION

[Test]

public void ShouldRouteToEchoAction()

{

var response = new HttpRequest("GET”,

"http://localhost/RestMvc/echo/hello"

).GetResponse();

Assert.That(response.StatusCode, Is.EqualTo(200));

Assert.That(response.Body, Is.EqualTo("hello"));

}

ValidateAnalyze Design

Code

Test

INSIGHT #2: TEST FIRST

ValidateAnalyze Design

Test

Code

INSIGHT #3: JUST ENOUGH CODE

Test

[TestFixture]

public class StackTest

{

[Test]

public void NewStackShouldBeEmpty()

{

var stack = new Stack();

Assert.That(stack.IsEmpty());

}

}

public class Stack

{

public bool IsEmpty()

{

return false;

}

}

ValidateAnalyze

DesignTest

Code

INSIGHT #4: TDD IS A DESIGN TECHNIQUE

Test

ValidateAnalyze

CodeTest

Design

INSIGHT #4: TDD IS A DESIGN TECHNIQUE

Test

ValidateAnalyze

CodeTest

Design

INSIGHT #4: TDD IS A DESIGN TECHNIQUE

Test

Refactoring

TDD is NOT:• A Testing Technique

TDD is:• A Design Technique

EVOLUTIONARY DESIGN

“Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.”

-Antoine de Saint-Exupery

Simple

Ain’t

Easy

EVOLUTIONARY DESIGN

Simple Design Rules

1. Must pass all tests

2. Must communicate intent

3. No duplication

4. Use fewest possible (classes, methods…)

BEHAVIOR DRIVEN DEVELOPMENT

There are only two hard problems in computer science:

• cache invalidation, and

• naming things.

-- Phil Karlton

ValidateAnalyze

CodeTest

DesignTest

ValidateAnalyze

CodeTest

Design Test

Specify

INSIGHT #5: TESTS AS COMMUNICATION

As a software development organization,

I want to have more predictability and adaptability

So that I can respond to change

Given a new requirementWhen I write the code for itThen I want to know whether I did the right thing

private Requirement requirement;

[Given(“a new requirement”)]public void GivenANewRequirement(){ requirement = new Requirement(); }

[When(“I write the code for it”)]public void WhenIWriteTheCodeForIt(){ requirement.Satisfy(); }

[Then(“I want to know .*”)]public void ThenIWantToKnowIfItWorked(){ Assert.That(requirement.IsSatisfied()); }

Time

Prod

uctiv

ityWHY NOT TDD?

We’ll never get here…

Our goal

TIC TAC TOE

https://github.com/bbyars/TicTacToe