Behavior-driven Development and Lambdaj

BDD + Lambdaj
Andreas Enbohm, Capgemini
@enbohm

BDD
• Behavior-driven development (BDD) is an
increasingly popular variation on test-driven
development, which helps developers think
more in terms of “executable specifications”
than in terms of conventional tests

Why use BDD?
• Only build feature that add real value
• Less wasted effort
• Better communication
• Higher quality, better tested product
• Traceability

BDD
• BDD describes TDD done well
- removes word ’test’
- replace it with
behaviour, examples, scenarios etc.
• Good habits;
1. Working outside-in
2. Using examples to clarify requirements
(scenarios)
3. Using a common (ubiquitous) language

BDD – Value Driven
• A good goal should add value to business
- increase revenue
- reduce cost
- avoid future cost
- protect revenue
”Increase revenue by allowing
customers to…”
”Prevent current customers
switching to competing product
by …”

BDD – What Does the Customer Need?
• Good teams push back!
- users tend to express requirements as implementations
- we need to find the business need!
We need caching
Why?
So that the page
loads fast
So that the
customer will buy
stuff on our site and
doesn’t leave page
Why?
Ok, so to increase the chance a customer
will buy [stuff] it need to be ’fast’. Caching
might be one way to achive this, but
compressing images might be more
effective. Or another way might be
loaders, or ..

BDD – Better understanding
• Working outside-in
- if you need to explain to a computer how to check the
requirement, you’ll need to be damn sure understand it
yourself
• Business black-box testing is often done manually!
- BDD enables automated acceptance testing
• Mininum effort /code to fulfull requirement

BDD – Common Language
• Common Language
- communication often the biggest overhead
- even bigger if you allow different dialects of terminology
- takes time but gains significant advantage

BDD - Stories
Story: Basic Purchase flow - User purchases a Grundpaket (id 21)
Narrative:
In order to attract new CDK customers
As a leading channel reseller
I want to provide an easy way to buy our products through our website
Goal come first
Stakeholder is
secondary
The feature must be
required to achieve this
goal

BDD - Scenarios
• The ’perfect’ bridge between the business-
facing and technology-facing sides of a team
Scenario: User selects a channel package for purchase (id 21.2)
Given address search is done with address street Hantverkaregatan streetNo 28 and city
Helsingborg on page url http://...
When user select totalpaketet by clicking on choose button
Then the user starts a purchase flow where the first step is called Grundpaket och box is
shown
Common language which is
reflected all way down in the
code

BDD - Java
• CDK use Jbehave
- lots of documentation
- uses Gherkin language

BDD – CDK Implementation
• No stories/scenarion from start
- Emma wrote a lot of BDD stories
- used by CDK as ’lightweight’ acceptance test
• Selenium
- browser automation
• Spring as embedded runner
- gives us DI
• Page template patterns (see code)

BDD – CDK Implementation
• Pros
- another way of thinking of test
- sentence instead of test (even for our Junit
tests)
- we could make our major refactoring with
confidence
• Cons
- selenium (engines)
- issus/bugs with JBehave (fetching
parameters, mapping to POJO)
- we should not come up with the goal

BDD
• Reports show 75%* less bugs and 30%* faster
to production

Lambdaj
• An internal DSL to manipulate collections
without loops
• Large part of business logic is always the
same; iteration over collections of business
objects to do a set of tasks
• Loops (especially nested and mixed with
conditions) are hard to read that to be written
• for loop is inherently serial

Lambdaj
• Business logic should be less technical and
closer to business fashion

Lambdaj
• Iterate over collections in order to:
- select
- aggregate
- sort
- filter
- group
- extract
- and more..

Lambdaj - Sort
List<Person> sortedByAgePersons = sort(persons, on(Person.class).getAge());
List<Person> sortedByAgePersons = new ArrayList<Person>(persons);
Collections.sort(sortedByAgePersons, new Comparator<Person>() {
public int compare(Person p1, Person p2) {
return Integer.valueOf(p1.getAge()).compareTo(p2.getAge());
}
});
Old Java style
Lambdaj

Lambdaj - Select
List<Sale> sales = select(sales, having(on(Sale.class).getBuyer(),
equalTo(selectMin(persons, on(Person.class).getAge()))));
Person youngest = null;
for (Person person : persons)
if (youngest == null || person.getAge() < youngest.getAge())
youngest = person;
List<Sale> buys = new ArrayList<Sale>();
for (Sale sale : sales)
if (sale.getBuyer().equals(youngest))
buys.add(sale);
Old Java style
Lambdaj

Lambdaj - Sum
Integer totalSumForStandaloneChannels =
sum(standaloneChannels,on(TvChannel.class).getPrice().getMonthlyFee());
Integer totalSumForStandaloneChannels = 0;
for (TvChannel channel: standaloneChannels) {
totalSumForStandaloneChannels += channel.getPrice.getMonthlyFee()
}
Old Java style
Lambdaj

Lambdaj - Group
Group<ChannelPackage> mutuallyExclusiveGroup =
group(selectedAddonPackages,
by(on(AddonChannelPackage.class).getGroup().getType()),
by(on(AddonChannelPackage.class).getGroup().getName()));
Don’t bother….
Old Java style
Lambdaj

Lambdaj - Index
Map<String, Car> carsByBrand = index(cars, on(Car.class).getBrand());
Map<String, Car> carsByBrand = new HashMap<String, Car>();
for (Car car : db.getCars())
carsByBrand.put(car.getBrand(), car);
Old Java style
Lambdaj

Lambdaj – Bulk Operations
List<Person> personInFamily = asList(new
Person(“Chuck"), new Person(“Lone Wolf"));
forEach(personInFamily).setLastName(“Norris");

Lambdaj - Closures
• Lambdaj Closures
Closure println = closure(); {
of(System.out).println(var(String.class));
}
//invoked by "closing" its free variable once:
println.apply("one");
//or more times:
println.each("one", "two", "three");

Behavior-driven Development and Lambdaj

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