Taking back BDD

Konstantin K. @everzet
Taking back
Behaviour Driven Development

The User-story
In order to spend more time socialising at the conference
instead of looking at the schedule
As a conference attendee
I want to create my personal schedule beforehand

Can you give me an
example of how you
would do it?

Scenarios in imperative style
Feature: Attendee selects talks to attend
In order to spend more time socialising at the conference instead of looking at the schedule
Scenario: Successfully selecting 1 talk
Given there is a conference "XP Conference"
And there is a "Specification" talk in first time period
When I open the "/conferences/xp" page
And I click "Add to my schedule" inside ".talk:contains('Specification')" block
Then I should see ".talk:contains('Specification')" inside ".personal-‐schedule" block
Scenario: Failing to select 2 talks into the time period
Given there is a conference "XP Conference"
And there is a "Specification" talk in the first time period
And there is a "Modelling" talk in the first time period
When I open the "/conferences/xp" page
And I click "Add to my schedule" inside ".talk:contains('Specification')" block
And I click "Add to my schedule" inside ".talk:contains('Modelling')" block
Then I should see ".talk:contains('Specification')" inside ".personal-‐schedule" block
But I should not see ".talk:contains('Modelling')" inside ".personal-‐schedule" block

And what if you are that
rare example of a
stakeholder without A
clear understanding of
TCP/ip & HTML5?

Scenarios in declarative style
Scenario: Successfully selecting 1 talk
Given there is a conference "Agile Conference"
When I choose the "Specification" talk
Then the "Specification" talk should be in my personal schedule
Scenario: Failing to select 2 talks into the same time period
Given there is a conference "Agile Conference"
And there is a "Modelling" talk in the first time period
When I choose the "Specification" talk
And I choose the "Modelling" talk
Then I should be told that time period is already taken by another talk

How do you actually
call all these things?

Scenario: Successfully selecting 1 talk from the 1 track conference for a single slot
Given a conference named "Agile Conference" with 1 track
And the "Specification" talk is scheduled for "10:30-‐11:30" slot on the conference track 1
When I choose the "Specification" talk for my personal schedule of this conference
Then the chosen talk for "10:30-‐11:30" slot of my schedule should be the "Specification"
Scenario: Being unable to select 2 talks into the same slot
Given a conference named "Agile Conference" with 2 tracks
And the "Modelling" talk is scheduled for "09:00-‐09:45" slot on the conference track 2
And I try to choose the "Modelling" talk for my personal schedule of this conference
Then I should be told that slot is already taken by another talk
Scenarios in ubiquitous language

“
– Eric Evans, Domain-Driven Design
A project faces serious problems when its
language is fractured. Domain experts use their
jargon while technical team members have their
own.

“
Translation blunts communication and makes
knowledge crunching anaemic.

{$}
BDD DDD
Translation???
{$} {$}

“
To cross-check all these decisions, we have to
constantly step through scenarios to conﬁrm that
we can solve application problems effectively.

“
A domain model is not a particular diagram; it is
the idea that the diagram is intended to convey.A
diagram can represent and communicate a model,
as can carefully written code, as can an English
sentence.

“Pushing for ubiquitous language hard enough
makes your examples a domain model.

Modelling by Example
BDD as it was meant to be done

Outside-in
UI
Domain core
Objects

“
– Vaughn Vernon, Implementing Domain-Driven Design
The application boundary, or inner hexagon, is
also the use case (or user story) boundary. In
other words, we should create use cases based on
application functional requirements, not on the
number of diverse clients or output mechanisms.

Middle-out
UI
Domain core
Objects

Domain core
Objects
1. Remove the UI

Domain core
Objects
1. Remove the UI
2. Go through the domain

Domain core
Objects
UI
1. Remove the UI
3. Add the UI back

Domain core
Objects
1. Remove the UI
3. Add the UI back
4. Go through the UI
UI

Example Of an Example
used as a domain model

Conference Feature

Domain Layer / Scenario #1

Domain Layer / Scenario #1 / Step #1

class AttendeeContext implements Context {
...
/**
* @Given a conference named :name with :count track(s)
*/
public function aConferenceNamedWithTrack($name, $count)
{
throw new PendingException();
}

...
/**
*/
{
$aConference =
}

...
/**
*/
{
$aConference = Conference::namedWithTracks($name, $count);
}

Conference
+ namedWithTracks()

conversation is your lead architect
Given a conference named "BDD eXchange" with 1 track
Given a conference named "BDD eXchange"
And this conference is planned to have 1 track
Conference
+ namedWithTracks()
Conference
+ named()
TrackPlanner
+ planTracks()
+ howManyTracks()

...
/**
* @Given the :talk talk is scheduled for :slot slot on the conference track :track
*/
public function talkIsScheduledForSlotOnTrack($talk, $slot, $track)
{
}

...
/**
*/
{
$talk = Talk::named($talk);
$slot = Slot::fromString($slot);
$track = Track::numbered($track);
}

...
/**
*/
{
$this-‐>conference-‐>scheduleTalk($talk, $slot, $track);
}

Conference
+ namedWithTracks()
+ scheduleTalk()
Talk
+ named()
Slot
+ fromString()
Track
+ numbered()

natural abstractions beat artificial ones
Bus
Car
<<interface>>
Vehicle
Trip to work

...
/**
* @When I choose the :talk talk for my personal schedule of this conference
*/
public function iChooseTheTalkForMyPersonalScheduleOfThisConference(Talk $talk)
{
}

...
/**
*/
{
$mySchedule = PersonalSchedule::ofConference($this-‐>conference);
}

...
/**
*/
{
$mySchedule = PersonalSchedule::ofConference($this-‐>conference);
$mySchedule-‐>chooseTalk($talk);
}

...
/**
*/
{
$this-‐>schedule = PersonalSchedule::ofConference($this-‐>conference);
$this-‐>schedule-‐>chooseTalk($talk);
}

Conference
+ namedWithTracks()
+ scheduleTalk()
Talk
+ named()
Slot
+ fromString()
Track
+ numbered()
PersonalSchedule
+ ofConference()
+ chooseTalk()
+ isTalkChosenForSlot()

It's ok to get it wrong
Conversation Understanding

...
/**
* @Then the chosen talk for :slot slot should be the :talk
*/
public function theChosenTalkForSlotShouldBeThe(Slot $slot, Talk $talk)
{
}

...
/**
* @Then the chosen talk for :slot slot should be the :talk
*/
public function theChosenTalkForSlotShouldBeThe(Slot $slot, Talk $talk)
{
assertTrue($this-‐>schedule-‐>isTalkChosenForSlot($talk, $slot));
}

Conference
+ namedWithTracks()
+ scheduleTalk()
Talk
+ named()
Slot
+ fromString()
Track
+ numbered()
PersonalSchedule
+ ofConference()
+ chooseTalk()
ScheduledTalk
+ isForTalk()
+ isScheduledFor()
+ hasSameSlotAs()

Planting Object-oriented software
Acceptance tests
Unit-tests
Domain core
Inner objects

Domain Layer / Scenario #2

Conference
+ namedWithTracks()
+ scheduleTalk()
Talk
+ named()
Slot
+ fromString()
Track
+ numbered()
PersonalSchedule
+ ofConference()
+ chooseTalk()
ScheduledTalk
+ isForTalk()
+ isScheduledFor()
+ hasSameSlotAs()
SlotIsAlreadyTaken

Domain Layer / both scenarios

Shorter stakeholder feedback loops
Domain
PERSISTENCE
UI
Days / weeks

UI is a controller for the domain

Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Scenario 6
DOMAIN
☑
☑
☑
☑
☑
☑

Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Scenario 6
DOMAIN UI
☑
☑
☑
☑
☑
☑

Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Scenario 6
DOMAIN
☑
☑
UI
☑
☑
☑
☑
☑
☑

Conference Feature critical paths
@critical

UI Layer / Scenario #1
@critical

UI Layer / Scenario #1 / Step #1
@critical

class WebAttendeeContext extends WebBasedContext {
...
/**
*/
{
$this-‐>conference = Conference::namedWithTracks($name, $count);
}

@critical

...
/**
*/
{
$this-‐>conference-‐>scheduleTalk($talk, $slot, $track);
}

@critical

...
/**
* @When I choose the :name talk for my personal schedule of this conference
*/
public function iChooseTheTalkForMyPersonalScheduleOfThisConference($name)
{
}

...
/**
*/
{
$this-‐>visit('/conferences/' . urlencode($this-‐>conference-‐>getName()));
}

...
/**
*/
{
$talkElement = $this-‐>find('css', ".talk:contains('$name')");
}

...
/**
*/
{
$talkElement-‐>clickLink('Add to my schedule');
}

...
/**
*/
{
}
...
/**
*/
{
// persist somehow?
}

...
/**
*/
{
}
...
/**
*/
{
$this-‐>conferenceRepository-‐>saveConference($this-‐>conference);
}

...
/**
*/
{
}
...
/**
*/
{
}

...
/**
*/
{
}
...
/**
* @Given a conference named :name with :count track(s) was planned
*/
{
}

...
/**
*/
{
}
...
/**
* @Given a conference named :name with :count track(s) was planned
*/
{
$this-‐>conferencePlanner-‐>planConference($this-‐>conference);
}

Coevolving Scenarios & Application code
Scenarios App code

@critical

...
/**
* @Then the chosen talk for :time slot should be the :name
*/
public function theChosenTalkForSlotShouldBeThe($name, $time)
{
}

...
/**
* @Then the chosen talk for :time slot should be the :name
*/
public function theChosenTalkForSlotShouldBeThe($name, $time)
{
$this-‐>assertElementText('css', ".my-‐schedule .talk:contains('$time')", $name);
}

Both Layers / both scenarios
@critical

"Hey, it does work" Testing pyramid
Acceptance
tests
Unit Tests
UI TESTS 1 scenario
2 scenarios
7 unit-test cases

“
– David West, Object Thinking
Model the problem domain and
the solution will take care of itself.

“Focus on discussing business problems and
the architecture will emerge naturally.

Thanks to
MathiasVerraes @mathiasverraes
Dan North @tastapod
Ciaran McNulty @CiaranMcNulty
Aslak Hellesøy @aslak_hellesoy
Marcello Duarte @_md
INVIQA @inviqa

Taking back BDD

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