Behaviour Driven DevelopmentWith NBehave

Linking User Stories and Domain Driven Design to Testing

David Ross

W: www.pebblesteps.com

E: willmation@gmail.com

Behavior Driven DevelopmentTools and techniques

Talk overview• What is BDD and how to use NBehave

Topics • What are high quality requirements?• Top down and Bottom up Testing • NBehave

• Using library• Using the test runner

• Top down design with Rhino.Mocks and Nbehave• Acceptance testing

Behavior Driven DevelopmentAnalysis/Design Methodology by Dan North

Response to:– confusion about Test Driven Development and

Test First Development– Lack of rigor around User Stories (Requirements)– Projects that generate documentation out of Unit

tests

Culminated in:– the BDD method for writing User Stories– JBehave unit testing framework

Behavior Driven Development

BDD is not:

• a testing framework or style of testing

• a method for writing tests

BDD is:

• A formalised template for User Stories

• Able to create testable User Stories since they

are defined in a formal manner

• Promotes “security” to a first call citizen in the

analysis process

Simple Trading applicationExcel spreadsheet replacement

• Allow Portfolio Manager to decide the

percentage split between Cash, Property

and Stock within the Portfolio

• Inform the Trader when the Portfolio needs

to be rebalanced (ie split in the pie has

changed significantly)

• Allow Operations to standardise Portfolio

names

Simple Trading application

Requirements

Test First Development

Small steps

Red - Analysis/Design Hat• Create a test that defines the expected outcome• Asking "What I want is...“

Green - Creative Hat (Fun part)• Experiment/Prototype/Build until the test passes

Refactor - Engineering• Refactor, refactor, refactor

Red Green Refactor

Test First DevelopmentHow easy is it to use TFD for the following

Requirement/Story•Value = Units * Market Price

•Increase the performance of the User Security module by automatically caching the user’s manager Id

•The system must email the Portfolio manager when the Portfolio needs to be rebalanced

•Build a web site so that customers can see the performance of the portfolio

Test First DevelopmentDo you feel guilty??

•Do you write a Failing unit test before every piece of code?

•Do you write a line of Unit Test code for EVERY line of production code?

Behavior Driven

How do you write a test when you don’t know where you are going?

Maybe we need requirements that are easy to write tests for?

RequirementsWhat are they

•Describes what a system should do but not how it will be done

•Contract between the implementation team and the analysis team

•Audience is typically the stake holders and not the development team

RequirementsPrecise and clear over verbose

We want requirements that

• Can be tested!!!

• Are attainable!!!

• Are traceable into code!!!

Requirements GatheringBDD merges two different approaches

User Stories•Short one or two line statement that maps to a few days of development work•Highly focused

Domain Driven Design•Ubiquitous language – Ensure business terminology permeates into code•Clear single definition (within the project) for each business concept - Account has a single meaning

Story TemplateAs a [User/Role]

I want [Behaviour]so that [I receive benefit]

ExampleAs a “Operations staff member”

I want “To create a Portfolio”so that “So that it can be traded”

BDD User StoriesFormal template for User Stories

BDD User StoriesFormal template for User Stories

Scenario TemplateGiven some initial context (the givens),

When an event occurs,then ensure some outcomes.

ExampleGiven “New portfolio is called Balanced

Fund”When “Portfolio already exists”then “Portfolio can no be created”

• .NET Library for writing automated BDD

style tests

• Fluent syntax for building up a BDD Style

User Stories

• Test runner that executes the stories and

generates a report listing the contents of the

stories

NBehave

What is it?

[Theme("Portfolio Maintenance")]

public class PortfolioMaintenanceStory

{

[Story]

public void portfolio_create_story () { ... }

[Story]

public void portfolio_delete_story() { ... }

}

Reference: NBehave.Narrator.Framework.dll

Creating a BDD ThemeCollection of related stories

var story = new Story("Create portfolio");

story.AsA(“Operations team member")

.IWant("To create a new portfolio on behalf of a

portfolio manager")

.SoThat("the portfolio manager can configure

the portfolio and the front office can trade");

Creating a Story Fluent interface to define the story

story.WithScenario("portfolio does not exist")

.Given("portfolio name is $name", "Aggressive

Fund")

.When("portfolio does not exist in the database")

.Then("new portfolio should be created");

story.WithScenario("portfolio already exists")

.Given("portfolio name is $name", "Aggressive Fund")

.When("portfolio already exists in database")

.Then("an error should occur");

Creating a ScenarioFluent interface to define the story

• Ouch we get an error???

• The scenario throws an exception – NBehave isn’t

validating any code

• Use Pending

story.WithScenario("portfolio does not exist")

.Pending("In progress")

.Given("portfolio name is $name", "Aggressive Fund")

.When("portfolio does not exist in the database")

.Then("new portfolio should be created");

Executing the testWith NBehave runner or mbUnit

StoryPending Scenario

Stubbed Scenario

Real Behaviour

Acceptance Test

Behavior Driven Development

Across the Project (Story) Life Cycle

1. Story2. Pending Scenario3. Stubbed Behavior Cycle (Red, Green, Refactor)

4. Real Behavior Cycle (Red, Green, Refactor)

5. Acceptance Test

Stubbing out the behaviorWith NBehave and Rhino.Mocks

Steps to generate an API

1. Go through the User story and find all the

domain objects

2. Create a class for each domain object but

don’t add state

3. Go through the User story and create a

find all the services that are required

(Repositories etc)

4. Create an interface for each service but

don’t add any methods

Steps to generate the API continued...

5. Slowly implement the story

6. Add domain object properties as required

7. Add methods signatures as required

8. Use Stubs to explore Inputs/Outputs to the

methods

Stubbing out the behaviorWith NBehave and Mocking

Stubbing example

string portfolioName = "";

Portfolio p = null;

var portfolioRepository =

MockRepository.GenerateStub<IPortfolioRepository>();

var portfolioService = MockRepository.GenerateStub<IPortfolioService>();

s.WithScenario("portfolio already exists")

.Given("portfolio name is $name", "Aggressive Fund", n => {

portfolioName = n;

p = new Portfolio { Name = portfolioName };

portfolioRepository.

Stub(x => x.FindPortfolioByName(portfolioName)).Return(p);

portfolioService.

Stub(X => X.CreatePortfolio(p)).Throw(new

ItemExistsException());

})

Create a new portfolio story

Stubbing example

.When("portfolio already exists in database",

() => Assert.IsNotNull(

portfolioRepository.FindPortfolioByName(portfolioNa

me))

)

.Then("new portfolio create should fail",

() => Assert.Throws<ItemExistsException>(() =>

portfolioService.CreatePortfolio(p))

);

Create a new portfolio story

TFD/BDD Comparison

Test First

• Bottom Up approach

• Lots of little steps working towards a solution

Output • Tests

Behavior Driven

• Top down approach• Design starting with

interfaces (using stubs)

• Back fill with code later

Output• API creation

NBehave

– test cases are compiled

– Must be created by developers or technical

testers

– Are created at the start of the project

Fitnesse

– User Acceptance tests are Wiki based and so

are dynamic

– Can be created by end users and business

analysts

– Can be created at the start of the project

– But are only “implemented” by the

development late in the SDLC

User Acceptance Test

Test Driven DevelopmentDevelopment/Testing Phases

User Stories

Behaviour Driven

Development

Unit &

Component

Test

System

Integration

Test

User

Acceptance

Test

Deployment

Verification

Test

Stubs

Domain

Model

Mocks

Implemented

Behaviour

No

Mocks

/Stubs

GUI Testing

Fitness

Fixtures to Specifications

Assert.IsTrue(component.IsValid)

component.IsValid.ShouldBeTrue()

Assert.Contains(s, “hello world”);

s.ShouldContains(“hello world”);

NBehave contains extension methods for NUnit, mbUnit,

xUnit

Loosing Assert from tests. Easier to read? For BAs, yes...

Fixtures to Specifications

[TestFixture] [Context]

[Test] [Specification]

[Context]

public class When_using_tokenized_stories

{

[Specification]

public void should_replace_token_with_value()

{}

Stories for BDD. Specifications for focussed

tests.

The word Test has become a dirty word...

Is it necessary?

Stories to documentationNBehave-Console.exe

PebbleSteps.NBehave.Stories.dll /o stories.txt

Theme: Trade Compliance

Story: Pretrade compliance check

As a Trader

I want verify a trade against the portfolio before I call the broker

So that the portfolio does not move out of compliance

Scenario: trade will move portfolio out of compliance

Given portfolio with name Balanced Fund

And asset allocation pie contains segments Cash 0.4, Stock 0.3, Property 0.3

And allocation pie 0.05

And portfolio contains Stock IBM 1, Cash GBP 1, Property SW5 1Hb 1, Stock BHP 1

When market prices are IBM 1, GBP 1, SW5 1Hb 1, BHP 1

Then portfolio value is 4

And portfolio constituents are Stock totalValue:2 percentOfPie:0.5 lower:0.25

upper:0.35, Cash totalValue:1 percentOfPie:0.25 lower:0.35 upper:0.45, Property totalValue:1

percentOfPie:0.25 lower:0.25 upper:0.35,

And portfolio is balanced

MSBuild

<UsingTaskAssemblyFile="NBehave.MSBuild.dll" TaskName="NBehave.MSBuild.NBehaveTask" />

<NBehaveTask

DryRun="false"

FailBuild="false"

StoryOutputPath="output.xml"

TestAssemblies="

PebbleSteps.NBehave.Stories.dll "

/>

Still in beta…

• The parameter regular expression is on [a-z][A-Z]

– $example0, $example1 – In story output first

parameter is printed twice

• Gallio integration/replacement of current story

runner

• Current story runner text output formatting is poor

– HTML

– or a XSLT for current XML output

• Occassional crash in the parsing engine that links

text to delegate parameters

What’s left to do?

• http://nbehave.org/

• http://www.codeplex.com/NBehave

• http://behaviour-driven.org/

• http://dannorth.net/

Code will be placed onto

www.pebblesteps.com

Questions?

More information