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Driving Design through Examples
Ciaran McNulty at PHPCon Poland 2015
Modelling by
Example
Combining BDD and DDD
concepts
Behaviour
Driven
Development
BDD helps with
1. Building things well
2. Building the right things
3. Building things for the right reason
... we will focus on 1 & 2
BDD is the art of using
examples in
conversations to
illustrate behaviour
— Liz Keogh
Why
Examples?
Requirements as Rules
We are starting a new budget airline flying between
London and Warsaw
→ Travellers can collect 1 point for every £1 they
spend on flights
→ 100 points can be redeemed for £10 off a future
flight
→ Flights are taxed at 20%
Rules are
Ambiguous
Ambiguity
→ When spending points do I still earn new points?
→ Can I redeem more than 100 points on one flight?
→ Is tax based on the discounted fare or the
original price of the fare?
Examples are
Unambiguous
Examples
If a flight from London to Warsaw costs £50:
→ If you pay cash it will cost £50 + £10 tax, and you
will earn 50 new points
→ If you pay entirely with points it will cost 500
points + £10 tax and you will earn 0 new points
→ If you pay with 100 points it will cost 100 points +
£40 + £10 tax and you will earn 0 new points
Examples are
Objectively
Testable
Gherkin
A formal language for
examples
You do not
have to use
Gherkin
Feature: Earning and spending points on flights
Rules:
- Travellers can collect 1 point for every £1 they spend on flights
- 100 points can be redeemed for £10 off a future flight
Scenario: Earning points when paying cash
Given ...
Scenario: Redeeming points for a discount on a flight
Given ...
Scenario: Paying for a flight entirely using points
Given ...
Gherkin steps
→ Given sets up context for a behaviour
→ When specifies some action
→ Then specifies some outcome
Action + Outcome = Behaviour
Scenario: Earning points when paying cash
Given a flight costs £50
When I pay with cash
Then I should pay £50 for the flight
And I should pay £10 tax
And I should get 50 points
Scenario: Redeeming points for a discount on a flight
Given a flight costs £50
When I pay with cash plus 100 points
Then I should pay £40 for the flight
And I should pay £10 tax
And I should pay 100 points
Scenario: Paying for a flight entirely using points
Given a flight costs £50
When I pay with points only
Then I should pay £0 for the flight
And I should pay £10 tax
And I should pay 500 points
Who writes examples?
Business expert
Testing expert
Development expert
All discussing the feature together
When to write scenarios
→ Before you start work on the feature
→ Not too long before!
→ Whenever you have access to the right people
Refining scenarios
→ When would this outcome not be true?
→ What other outcomes are there?
→ But what would happen if...?
→ Does this implementation detail matter?
Scenarios are
not Contracts
Scenarios
→ Create a shared understanding of a feature
→ Give a starting definition of done
→ Provide an objective indication of how to test a
feature
Domain
Driven Design
DDD tackles complexity
by focusing the team's
attention on knowledge
of the domain
— Eric Evans
Invest time in
understanding
the business
Ubiquitous Language
→ A shared way of speaking about domain concepts
→ Reduces the cost of translation when business
and development communicate
→ Try to establish and use terms the business will
understand
Modelling by
Example
By embedding Ubiquitous
Language in your scenarios,
your scenarios naturally
become your domain model
— Konstantin Kudryashov (@everzet)
Principles
→ The best way to understand the domain is by
discussing examples
→ Write scenarios that capture ubiquitous language
→ Write scenarios that illustrate real situations
→ Directly drive the code model from those
examples
Directly
driving code
with Behat?
Layered architecture
UI testing with Behat
UI tests
→ Slow to execute
→ Brittle
→ Don't let you think about the code
Test the domain first
Scenario: Earning points when paying cash
Given a flight costs £50
When I pay with cash
Then I should pay £50 for the flight
And I should pay £10 tax
And I should get 50 points
Scenario: Redeeming points for a discount on a flight
Given a flight costs £50
When I pay with cash plus 100 points
Then I should pay £40 for the flight
And I should pay £10 tax
And I should pay 100 points
Scenario: Paying for a flight entirely using points
Given a flight costs £50
When I pay with points only
Then I should pay £0 for the flight
And I should pay £10 tax
And I should pay 500 points
Add realistic
details
Background:
Given a flight from "London" to "Manchester" costs £50
Scenario: Earning points when paying cash
When I fly from "London" to "Manchester"
And I pay with cash
Then I should pay £50 for the flight
And I should pay £10 tax
And I should get 50 points
Actively seek
terms from
the domain
→ What words do you use to talk about these
things?
→ Points? Paying? Cash Fly?
→ Is the cost really attached to a flight?
→ Do you call this thing "tax"?
→ How do you think about these things?
Get good at
listening
Lessons from the conversation
→ Price belongs to a Fare for a specific Route
→ Flight is independently assigned to a Route
→ Some sort of fare listing system controls Fares
→ I get quoted a cost at the point I purchase a ticket
This is really useful to know!
Background:
Given a flight "XX-100" flies the "LHR" to "MAN" route
And the current listed fare for the "LHR" to "MAN" route is £50
Scenario: Earning points when paying cash
When I am issued a ticket on flight "XX-100"
And I pay £50 cash for the ticket
Then the ticket should be completely paid
And the ticket should be worth 50 loyalty points
Driving the
domain model
with Behat
Configure a Behat suite
default:
suites:
core:
contexts: [ FlightsContext ]
Create a context
class FlightsContext implements Context
{
/**
* @Given a flight :arg1 flies the :arg2 to :arg3 route
*/
public function aFlightFliesTheRoute($arg1, $arg2, $arg3)
{
throw new PendingException();
}
// ...
}
Run Behat
Model values
as Value
Objects
class FlightsContext implements Context
{
/**
* @Given a flight :flightnumber flies the :origin to :destination route
*/
public function aFlightFliesTheRoute($flightnumber, $origin, $destination)
{
$this->flight = new Flight(
FlightNumber::fromString($flightnumber),
Route::between(
Airport::fromCode($origin),
Airport::fromCode($destination)
)
);
}
// ...
}
Transformations
/**
* @Transform :flightnumber
*/
public function transformFlightNumber($number)
{
return FlightNumber::fromString($number);
}
/**
* @Transform :origin
* @Transform :destination
*/
public function transformAirport($code)
{
return Airport::fromCode($code);
}
/**
* @Given a flight :flightnumber flies the :origin to :destination route
*/
public function aFlightFliesTheRoute(
FlightNumber $flightnumber,
Airport $origin,
Airport $destination
)
{
$this->flight = new Flight(
$flightnumber, Route::between($origin, $destination)
);
}
> vendor/bin/behat
PHP Fatal error: Class 'Flight' not found
Describe
objects with
PhpSpec
class AirportSpec extends ObjectBehavior
{
function it_can_be_represented_as_a_string()
{
$this->beConstructedFromCode('LHR');
$this->asCode()->shouldReturn('LHR');
}
function it_cannot_be_created_with_invalid_code()
{
$this->beConstructedFromCode('1234566XXX');
$this->shouldThrow(Exception::class)->duringInstantiation();
}
}
class Airport
{
private $code;
private function __construct($code)
{
if (!preg_match('/^[A-Z]{3}$/', $code)) {
throw new InvalidArgumentException('Code is not valid');
}
$this->code = $code;
}
public static function fromCode($code)
{
return new Airport($code);
}
public function asCode()
{
return $this->code;
}
}
/**
* @Given the current listed fare for the :arg1 to :arg2 route is £:arg3
*/
public function theCurrentListedFareForTheToRouteIsPs($arg1, $arg2, $arg3)
{
throw new PendingException();
}
Model boundaries
with Interfaces
interface FareList
{
public function listFare(Route $route, Fare $fare);
}
Create in-memory versions for testing
namespace Fake;
class FareList implements FareList
{
private $fares = [];
public function listFare(Route $route, Fare $fare)
{
$this->fares[$route->asString()] = $fare;
}
}
/**
* @Given the current listed fare for the :origin to :destination route is £:fare
*/
public function theCurrentListedFareForTheToRouteIsPs(
Airport $origin,
Airport $destination,
Fare $fare
)
{
$this->fareList = new FakeFareList();
$this->fareList->listFare(
Route::between($origin, $destination),
Fare::fromString($fare)
);
}
Run Behat
/**
* @When Iam issued a ticket on flight :arg1
*/
public function iAmIssuedATicketOnFlight($arg1)
{
throw new PendingException();
}
/**
* @When I am issued a ticket on flight :flight
*/
public function iAmIssuedATicketOnFlight()
{
$ticketIssuer = new TicketIssuer($this->fareList);
$this->ticket = $ticketIssuer->issueOn($this->flight);
}
> vendor/bin/behat
PHP Fatal error: Class 'TicketIssuer' not found
class TicketIssuerSpec extends ObjectBehavior
{
function it_can_issue_a_ticket_for_a_flight(Flight $flight)
{
$this->issueOn($flight)->shouldHaveType(Ticket::class);
}
}
class TicketIssuer
{
public function issueOn(Flight $flight)
{
return Ticket::costing(Fare::fromString('10000.00'));
}
}
Run Behat
/**
* @When I pay £:fare cash for the ticket
*/
public function iPayPsCashForTheTicket(Fare $fare)
{
$this->ticket->pay($fare);
}
PHP Fatal error: Call to undefined method Ticket::pay()
class TicketSpec extends ObjectBehavior
{
function it_can_be_paid()
{
$this->pay(Fare::fromString("10.00"));
}
}
class Ticket
{
public function pay(Fare $fare)
{
}
}
Run Behat
The model will be
anaemicUntil you get to Then
/**
* @Then the ticket should be completely paid
*/
public function theTicketShouldBeCompletelyPaid()
{
throw new PendingException();
}
/**
* @Then the ticket should be completely paid
*/
public function theTicketShouldBeCompletelyPaid()
{
assert($this->ticket->isCompletelyPaid() == true);
}
PHP Fatal error: Call to undefined method Ticket::isCompletelyPaid()
class TicketSpec extends ObjectBehavior
{
function let()
{
$this->beConstructedCosting(Fare::fromString("50.00"));
}
function it_is_not_completely_paid_initially()
{
$this->shouldNotBeCompletelyPaid();
}
function it_can_be_paid_completely()
{
$this->pay(Fare::fromString("50.00"));
$this->shouldBeCompletelyPaid();
}
}
class Ticket
{
private $fare;
// ...
public function pay(Fare $fare)
{
$this->fare = $this->fare->deduct($fare);
}
public function isCompletelyPaid()
{
return $this->fare->isZero();
}
}
class FareSpec extends ObjectBehavior
{
function let()
{
$this->beConstructedFromString('100.00');
}
function it_can_deduct_an_amount()
{
$this->deduct(Fare::fromString('10'))->shouldBeLike(Fare::fromString('90.00'));
}
}
class Fare
{
private $pence;
private function __construct($pence)
{
$this->pence = $pence;
}
// ...
public function deduct(Fare $amount)
{
return new Fare($this->pence - $amount->pence);
}
}
class FareSpec extends ObjectBehavior
{
// ...
function it_knows_when_it_is_zero()
{
$this->beConstructedFromString('0.00');
$this->shouldBeZero();
}
function it_is_not_zero_when_it_has_a_value()
{
$this->beConstructedFromString('10.00');
$this->shouldNotBeZero();
}
}
class Fare
{
private $pence;
private function __construct($pence)
{
$this->pence = $pence;
}
// ...
public function isZero()
{
return $this->pence == 0;
}
}
Run Behat
class TicketIssuerSpec extends ObjectBehavior
{
function it_issues_a_ticket_with_the_correct_fare(FareList $fareList)
{
$route = Route::between(Airport::fromCode('LHR'), Airport::fromCode('MAN'));
$flight = new Flight(FlightNumber::fromString('XX001'), $route);
$fareList->findFareFor($route)->willReturn(Fare::fromString('50'));
$this->beConstructedWith($fareList);
$this->issueOn($flight)->shouldBeLike(Ticket::costing(Fare::fromString('50')));
}
}
class TicketIssuer
{
private $fareList;
public function __construct(FareList $fareList)
{
$this->fareList = $fareList;
}
public function issueOn(Flight $flight)
{
return Ticket::costing($this->fareList->findFareFor($flight->getRoute()));
}
}
interface FareList
{
public function listFare(Route $route, Fare $fare);
public function findFareFor(Route $route);
}
class FareList implements FareList
{
private $fares = [];
public function listFare(Route $route, Fare $fare)
{
$this->fares[$route->asString()] = $fare;
}
public function findFareFor(Route $route)
{
return $this->fares[$route->asString()];
}
}
Run Behat
/**
* @Then I the ticket should be worth :points loyalty points
*/
public function iTheTicketShouldBeWorthLoyaltyPoints(Points $points)
{
assert($this->ticket->getPoints() == $points);
}
class FareSpec extends ObjectBehavior
{
function let()
{
$this->beConstructedFromString('100.00');
}
// ...
function it_calculates_points()
{
$this->getPoints()->shouldBeLike(Points::fromString('100'));
}
}
class TicketSpec extends ObjectBehavior
{
function let()
{
$this->beConstructedCosting(Fare::fromString("100.00"));
}
// ...
function it_gets_points_from_original_fare()
{
$this->pay(Fare::fromString("50"));
$this->getPoints()->shouldBeLike(Points::fromString('100'));
}
}
<?php
class Ticket
{
private $revenueFare;
private $fare;
private function __construct(Fare $fare)
{
$this->revenueFare = $fare;
$this->fare = $fare;
}
// ...
public function getPoints()
{
return $this->revenueFare->getPoints();
}
}
Run Behat
Where is our
domain
model?
Feature: Earning and spending points on flights
Rules:
- Travellers can collect 1 point for every £1 they spend on flights
- 100 points can be redeemed for £10 off a future flight
Background:
Given a flight "XX-100" flies the "LHR" to "MAN" route
And the current listed fare for the "LHR" to "MAN" route is £50
Scenario: Earning points when paying cash
When I am issued a ticket on flight "XX-100"
And I pay £50 cash for the ticket
Then the ticket should be completely paid
And I the ticket should be worth 50 loyalty points
> bin/phpspec run -f pretty
Airport
10 ✔ can be represented as a string
16 ✔ cannot be created with invalid code
Fare
15 ✔ can deduct an amount
20 ✔ knows when it is zero
26 ✔ is not zero when it has a value
31 ✔ calculates points
FlightNumber
10 ✔ can be represented as a string
Flight
13 ✔ exposes route
Points
10 ✔ is constructed from string
Route
12 ✔ has a string representation
TicketIssuer
16 ✔ issues a ticket with the correct fare
Ticket
15 ✔ is not completely paid initially
20 ✔ is not paid completely if it is partly paid
27 ✔ can be paid completely
34 ✔ gets points from original fare
UI Testing
With the domain already modelled
→ UI tests do not have to be comprehensive
→ Can focus on intractions and UX
→ Actual UI code is easier to write!
default:
suites:
core:
contexts: [ FlightsContext ]
web:
contexts: [ WebFlightsContext ]
filters: { tags: @ui }
Feature: Earning and spending points on flights
Scenario: Earning points when paying cash
Given ...
@ui
Scenario: Redeeming points for a discount on a flight
Given ...
Scenario: Paying for a flight entirely using points
Given ...
Modelling by Example
→ Focuses attention on use cases
→ Helps developers understand core business
domains
→ Encourages layered architecture
→ Speeds up test suites
Use it when
→ Project is core to your business
→ You are likely to support business changes in the
future
→ You can have conversations with stakeholders
Do not use when...
→ Not core to the business
→ Prototype or short-term project
→ It can be thrown away when the business
changes
→ You have no access to business experts (but try
and change this)
Thank you!
@ciaranmcnulty
Inviqa / Sensio Labs UK / Session Digital / iKOS
https://joind.in/16243
Questions?

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Driving Design through Examples - PhpCon PL 2015

  • 1. Driving Design through Examples Ciaran McNulty at PHPCon Poland 2015
  • 4. BDD helps with 1. Building things well 2. Building the right things 3. Building things for the right reason ... we will focus on 1 & 2
  • 5. BDD is the art of using examples in conversations to illustrate behaviour — Liz Keogh
  • 7. Requirements as Rules We are starting a new budget airline flying between London and Warsaw → Travellers can collect 1 point for every £1 they spend on flights → 100 points can be redeemed for £10 off a future flight → Flights are taxed at 20%
  • 9. Ambiguity → When spending points do I still earn new points? → Can I redeem more than 100 points on one flight? → Is tax based on the discounted fare or the original price of the fare?
  • 11. Examples If a flight from London to Warsaw costs £50: → If you pay cash it will cost £50 + £10 tax, and you will earn 50 new points → If you pay entirely with points it will cost 500 points + £10 tax and you will earn 0 new points → If you pay with 100 points it will cost 100 points + £40 + £10 tax and you will earn 0 new points
  • 14. You do not have to use Gherkin
  • 15. Feature: Earning and spending points on flights Rules: - Travellers can collect 1 point for every £1 they spend on flights - 100 points can be redeemed for £10 off a future flight Scenario: Earning points when paying cash Given ... Scenario: Redeeming points for a discount on a flight Given ... Scenario: Paying for a flight entirely using points Given ...
  • 16. Gherkin steps → Given sets up context for a behaviour → When specifies some action → Then specifies some outcome Action + Outcome = Behaviour
  • 17. Scenario: Earning points when paying cash Given a flight costs £50 When I pay with cash Then I should pay £50 for the flight And I should pay £10 tax And I should get 50 points Scenario: Redeeming points for a discount on a flight Given a flight costs £50 When I pay with cash plus 100 points Then I should pay £40 for the flight And I should pay £10 tax And I should pay 100 points Scenario: Paying for a flight entirely using points Given a flight costs £50 When I pay with points only Then I should pay £0 for the flight And I should pay £10 tax And I should pay 500 points
  • 18. Who writes examples? Business expert Testing expert Development expert All discussing the feature together
  • 19. When to write scenarios → Before you start work on the feature → Not too long before! → Whenever you have access to the right people
  • 20. Refining scenarios → When would this outcome not be true? → What other outcomes are there? → But what would happen if...? → Does this implementation detail matter?
  • 22. Scenarios → Create a shared understanding of a feature → Give a starting definition of done → Provide an objective indication of how to test a feature
  • 24. DDD tackles complexity by focusing the team's attention on knowledge of the domain — Eric Evans
  • 26. Ubiquitous Language → A shared way of speaking about domain concepts → Reduces the cost of translation when business and development communicate → Try to establish and use terms the business will understand
  • 28. By embedding Ubiquitous Language in your scenarios, your scenarios naturally become your domain model — Konstantin Kudryashov (@everzet)
  • 29. Principles → The best way to understand the domain is by discussing examples → Write scenarios that capture ubiquitous language → Write scenarios that illustrate real situations → Directly drive the code model from those examples
  • 33. UI tests → Slow to execute → Brittle → Don't let you think about the code
  • 34. Test the domain first
  • 35. Scenario: Earning points when paying cash Given a flight costs £50 When I pay with cash Then I should pay £50 for the flight And I should pay £10 tax And I should get 50 points Scenario: Redeeming points for a discount on a flight Given a flight costs £50 When I pay with cash plus 100 points Then I should pay £40 for the flight And I should pay £10 tax And I should pay 100 points Scenario: Paying for a flight entirely using points Given a flight costs £50 When I pay with points only Then I should pay £0 for the flight And I should pay £10 tax And I should pay 500 points
  • 37. Background: Given a flight from "London" to "Manchester" costs £50 Scenario: Earning points when paying cash When I fly from "London" to "Manchester" And I pay with cash Then I should pay £50 for the flight And I should pay £10 tax And I should get 50 points
  • 39. → What words do you use to talk about these things? → Points? Paying? Cash Fly? → Is the cost really attached to a flight? → Do you call this thing "tax"? → How do you think about these things?
  • 41. Lessons from the conversation → Price belongs to a Fare for a specific Route → Flight is independently assigned to a Route → Some sort of fare listing system controls Fares → I get quoted a cost at the point I purchase a ticket This is really useful to know!
  • 42. Background: Given a flight "XX-100" flies the "LHR" to "MAN" route And the current listed fare for the "LHR" to "MAN" route is £50 Scenario: Earning points when paying cash When I am issued a ticket on flight "XX-100" And I pay £50 cash for the ticket Then the ticket should be completely paid And the ticket should be worth 50 loyalty points
  • 44. Configure a Behat suite default: suites: core: contexts: [ FlightsContext ]
  • 45. Create a context class FlightsContext implements Context { /** * @Given a flight :arg1 flies the :arg2 to :arg3 route */ public function aFlightFliesTheRoute($arg1, $arg2, $arg3) { throw new PendingException(); } // ... }
  • 48. class FlightsContext implements Context { /** * @Given a flight :flightnumber flies the :origin to :destination route */ public function aFlightFliesTheRoute($flightnumber, $origin, $destination) { $this->flight = new Flight( FlightNumber::fromString($flightnumber), Route::between( Airport::fromCode($origin), Airport::fromCode($destination) ) ); } // ... }
  • 49. Transformations /** * @Transform :flightnumber */ public function transformFlightNumber($number) { return FlightNumber::fromString($number); } /** * @Transform :origin * @Transform :destination */ public function transformAirport($code) { return Airport::fromCode($code); }
  • 50. /** * @Given a flight :flightnumber flies the :origin to :destination route */ public function aFlightFliesTheRoute( FlightNumber $flightnumber, Airport $origin, Airport $destination ) { $this->flight = new Flight( $flightnumber, Route::between($origin, $destination) ); }
  • 51. > vendor/bin/behat PHP Fatal error: Class 'Flight' not found
  • 53. class AirportSpec extends ObjectBehavior { function it_can_be_represented_as_a_string() { $this->beConstructedFromCode('LHR'); $this->asCode()->shouldReturn('LHR'); } function it_cannot_be_created_with_invalid_code() { $this->beConstructedFromCode('1234566XXX'); $this->shouldThrow(Exception::class)->duringInstantiation(); } }
  • 54. class Airport { private $code; private function __construct($code) { if (!preg_match('/^[A-Z]{3}$/', $code)) { throw new InvalidArgumentException('Code is not valid'); } $this->code = $code; } public static function fromCode($code) { return new Airport($code); } public function asCode() { return $this->code; } }
  • 55.
  • 56. /** * @Given the current listed fare for the :arg1 to :arg2 route is £:arg3 */ public function theCurrentListedFareForTheToRouteIsPs($arg1, $arg2, $arg3) { throw new PendingException(); }
  • 58. interface FareList { public function listFare(Route $route, Fare $fare); }
  • 59. Create in-memory versions for testing namespace Fake; class FareList implements FareList { private $fares = []; public function listFare(Route $route, Fare $fare) { $this->fares[$route->asString()] = $fare; } }
  • 60. /** * @Given the current listed fare for the :origin to :destination route is £:fare */ public function theCurrentListedFareForTheToRouteIsPs( Airport $origin, Airport $destination, Fare $fare ) { $this->fareList = new FakeFareList(); $this->fareList->listFare( Route::between($origin, $destination), Fare::fromString($fare) ); }
  • 62. /** * @When Iam issued a ticket on flight :arg1 */ public function iAmIssuedATicketOnFlight($arg1) { throw new PendingException(); }
  • 63. /** * @When I am issued a ticket on flight :flight */ public function iAmIssuedATicketOnFlight() { $ticketIssuer = new TicketIssuer($this->fareList); $this->ticket = $ticketIssuer->issueOn($this->flight); }
  • 64. > vendor/bin/behat PHP Fatal error: Class 'TicketIssuer' not found
  • 65. class TicketIssuerSpec extends ObjectBehavior { function it_can_issue_a_ticket_for_a_flight(Flight $flight) { $this->issueOn($flight)->shouldHaveType(Ticket::class); } }
  • 66. class TicketIssuer { public function issueOn(Flight $flight) { return Ticket::costing(Fare::fromString('10000.00')); } }
  • 68. /** * @When I pay £:fare cash for the ticket */ public function iPayPsCashForTheTicket(Fare $fare) { $this->ticket->pay($fare); }
  • 69. PHP Fatal error: Call to undefined method Ticket::pay()
  • 70. class TicketSpec extends ObjectBehavior { function it_can_be_paid() { $this->pay(Fare::fromString("10.00")); } }
  • 71. class Ticket { public function pay(Fare $fare) { } }
  • 73. The model will be anaemicUntil you get to Then
  • 74. /** * @Then the ticket should be completely paid */ public function theTicketShouldBeCompletelyPaid() { throw new PendingException(); }
  • 75. /** * @Then the ticket should be completely paid */ public function theTicketShouldBeCompletelyPaid() { assert($this->ticket->isCompletelyPaid() == true); }
  • 76. PHP Fatal error: Call to undefined method Ticket::isCompletelyPaid()
  • 77. class TicketSpec extends ObjectBehavior { function let() { $this->beConstructedCosting(Fare::fromString("50.00")); } function it_is_not_completely_paid_initially() { $this->shouldNotBeCompletelyPaid(); } function it_can_be_paid_completely() { $this->pay(Fare::fromString("50.00")); $this->shouldBeCompletelyPaid(); } }
  • 78. class Ticket { private $fare; // ... public function pay(Fare $fare) { $this->fare = $this->fare->deduct($fare); } public function isCompletelyPaid() { return $this->fare->isZero(); } }
  • 79. class FareSpec extends ObjectBehavior { function let() { $this->beConstructedFromString('100.00'); } function it_can_deduct_an_amount() { $this->deduct(Fare::fromString('10'))->shouldBeLike(Fare::fromString('90.00')); } }
  • 80. class Fare { private $pence; private function __construct($pence) { $this->pence = $pence; } // ... public function deduct(Fare $amount) { return new Fare($this->pence - $amount->pence); } }
  • 81. class FareSpec extends ObjectBehavior { // ... function it_knows_when_it_is_zero() { $this->beConstructedFromString('0.00'); $this->shouldBeZero(); } function it_is_not_zero_when_it_has_a_value() { $this->beConstructedFromString('10.00'); $this->shouldNotBeZero(); } }
  • 82. class Fare { private $pence; private function __construct($pence) { $this->pence = $pence; } // ... public function isZero() { return $this->pence == 0; } }
  • 84. class TicketIssuerSpec extends ObjectBehavior { function it_issues_a_ticket_with_the_correct_fare(FareList $fareList) { $route = Route::between(Airport::fromCode('LHR'), Airport::fromCode('MAN')); $flight = new Flight(FlightNumber::fromString('XX001'), $route); $fareList->findFareFor($route)->willReturn(Fare::fromString('50')); $this->beConstructedWith($fareList); $this->issueOn($flight)->shouldBeLike(Ticket::costing(Fare::fromString('50'))); } }
  • 85. class TicketIssuer { private $fareList; public function __construct(FareList $fareList) { $this->fareList = $fareList; } public function issueOn(Flight $flight) { return Ticket::costing($this->fareList->findFareFor($flight->getRoute())); } }
  • 86. interface FareList { public function listFare(Route $route, Fare $fare); public function findFareFor(Route $route); }
  • 87. class FareList implements FareList { private $fares = []; public function listFare(Route $route, Fare $fare) { $this->fares[$route->asString()] = $fare; } public function findFareFor(Route $route) { return $this->fares[$route->asString()]; } }
  • 89. /** * @Then I the ticket should be worth :points loyalty points */ public function iTheTicketShouldBeWorthLoyaltyPoints(Points $points) { assert($this->ticket->getPoints() == $points); }
  • 90. class FareSpec extends ObjectBehavior { function let() { $this->beConstructedFromString('100.00'); } // ... function it_calculates_points() { $this->getPoints()->shouldBeLike(Points::fromString('100')); } }
  • 91. class TicketSpec extends ObjectBehavior { function let() { $this->beConstructedCosting(Fare::fromString("100.00")); } // ... function it_gets_points_from_original_fare() { $this->pay(Fare::fromString("50")); $this->getPoints()->shouldBeLike(Points::fromString('100')); } }
  • 92. <?php class Ticket { private $revenueFare; private $fare; private function __construct(Fare $fare) { $this->revenueFare = $fare; $this->fare = $fare; } // ... public function getPoints() { return $this->revenueFare->getPoints(); } }
  • 95. Feature: Earning and spending points on flights Rules: - Travellers can collect 1 point for every £1 they spend on flights - 100 points can be redeemed for £10 off a future flight Background: Given a flight "XX-100" flies the "LHR" to "MAN" route And the current listed fare for the "LHR" to "MAN" route is £50 Scenario: Earning points when paying cash When I am issued a ticket on flight "XX-100" And I pay £50 cash for the ticket Then the ticket should be completely paid And I the ticket should be worth 50 loyalty points
  • 96. > bin/phpspec run -f pretty Airport 10 ✔ can be represented as a string 16 ✔ cannot be created with invalid code Fare 15 ✔ can deduct an amount 20 ✔ knows when it is zero 26 ✔ is not zero when it has a value 31 ✔ calculates points FlightNumber 10 ✔ can be represented as a string Flight 13 ✔ exposes route Points 10 ✔ is constructed from string Route 12 ✔ has a string representation TicketIssuer 16 ✔ issues a ticket with the correct fare Ticket 15 ✔ is not completely paid initially 20 ✔ is not paid completely if it is partly paid 27 ✔ can be paid completely 34 ✔ gets points from original fare
  • 98. With the domain already modelled → UI tests do not have to be comprehensive → Can focus on intractions and UX → Actual UI code is easier to write!
  • 99. default: suites: core: contexts: [ FlightsContext ] web: contexts: [ WebFlightsContext ] filters: { tags: @ui }
  • 100. Feature: Earning and spending points on flights Scenario: Earning points when paying cash Given ... @ui Scenario: Redeeming points for a discount on a flight Given ... Scenario: Paying for a flight entirely using points Given ...
  • 101. Modelling by Example → Focuses attention on use cases → Helps developers understand core business domains → Encourages layered architecture → Speeds up test suites
  • 102. Use it when → Project is core to your business → You are likely to support business changes in the future → You can have conversations with stakeholders
  • 103. Do not use when... → Not core to the business → Prototype or short-term project → It can be thrown away when the business changes → You have no access to business experts (but try and change this)
  • 104. Thank you! @ciaranmcnulty Inviqa / Sensio Labs UK / Session Digital / iKOS https://joind.in/16243 Questions?