Tests doubles: the motion picture

Test doubles explained

Transcript

1. TDD 101 6. Test doubles: the motion picture
2. Test doubles: 
 the motion picture
3. The plot
4. You want to test an object that uses collaborators…
5. You need to isolate its behaviour from that of its collaborators
6. Then, you’ll need… test doubles
7. The argument
8. A unit of software Can be a query: returns a response Can be a command: produces a change in the state of the system You should test the results of the behavior
9. When you test it You want to prove that the behavior: • Is produced by the code of the unit of software • Is not influenced by any other factor
10. So, you need to control the behavior of collaborators Cancelling: no behavior at all Controlling: knowing exactly what they are doing (by means of programming it)
11. The cast
12. Dummy No behavior Only interface
13. namespace Dojo\HappyBirthday\Logger; interface SimpleLogger { public function log(string $channel, string $message): void; }
14. namespace Tests\Dojo\HappyBirthday\Double; use Dojo\HappyBirthday\Logger\SimpleLogger; class LoggerDummy implements SimpleLogger { public function log(string $channel, string $message): void { } }
15. namespace Tests\Dojo\HappyBirthday; use Dojo\HappyBirthday\SendGreetings; use PHPUnit\Framework\TestCase; class SendGreetingsTest extends TestCase { public function testSendGreetingToCustomersWhenIsTheirBirthday() { $clockService = $this->getClockServiceStub(); $logger = $this->getLoggerDummy(); $customerRepository = $this->getCustomerRepositoryStub(); $mailer = $this->getMailerSpy([ new Customer('cust1@example.com'), new Customer('cust2@example.com'), new Customer('cust3@example.com') ]); $sendGreetings = new SendGreetings( $clockService, $customerRepository, $mailer, $logger ); $sendGreetings->execute(); $this->assertEquals(3. $mailer->getMessagesSent()); } }
16. Stub Programmed behavior
17. namespace Dojo\HappyBirthday\Clock; use DateTimeImmutable; interface ClockService { public function currentDate(): DateTimeImmutable; }
18. namespace Tests\Dojo\HappyBirthday\Double; use DateTimeImmutable; use Dojo\HappyBirthday\Clock\ClockService; class ClockServiceStub implements ClockService { /** @var DateTimeImmutable */ private $dateTime; public function __construct(DateTimeImmutable $dateTime) { $this->dateTime = $dateTime; } public function currentDate() : DateTimeImmutable { return $this->dateTime; } }
19. namespace Tests\Dojo\HappyBirthday; use Dojo\HappyBirthday\SendGreetings; use PHPUnit\Framework\TestCase; class SendGreetingsTest extends TestCase { public function testSendGreetingToCustomersWhenIsTheirBirthday() { $clockService = $this->getClockServiceStub(); $logger = $this->getLoggerDummy(); $customerRepository = $this->getCustomerRepositoryStub(); $mailer = $this->getMailerSpy([ new Customer('cust1@example.com'), new Customer('cust2@example.com'), new Customer('cust3@example.com') ]); $sendGreetings = new SendGreetings( $clockService, $customerRepository, $mailer, $logger ); $sendGreetings->execute(); $this->assertEquals(3. $mailer->getMessagesSent()); } }
20. Fake Behavior implementation… but best suited for testing Needs its own tests
21. namespace Dojo\HappyBirthday\Contacts; interface ContactRepositoryInterface { public function retrieveById(UUid $uuid): Contact; }
22. namespace Dojo\HappyBirthday\Contacts; class InMemoryContactRepository implements ContactRepository { public function retrieveById(UUid $uuid): Contact { } }
23. Spy Registers how is used Fragility (coupling)
24. interface Mailer { public function send(Message $message) : void; }
25. class MailerSpy implements Mailer { private $calls = 0; public function send(Message $message) : void { $this->calls++; } public function getCalls() { return $this->calls; } }
26. Mock Has expectations about how is used Takes assertions
 away from the test Fragility (coupling)
27. Taxonomy
28. Behavior Knowledge
29. test doubles by behavior dummy stub fake no behavior fixed complete Applies to any kind of double by knowledge
30. test doubles by knowledge passive spy mock Applies to any kind of double by behavior knows
 nothing registers
 use has
 expectations
31. How to
32. i
33. Design principles Dem SRP OCP DIP ISP LSP DRY Yagni
34. The “real” object Should have: • No behavior • No side effects • Immutability
35. Self-shunt Exploratory and sparse use Simple interface
36. class ServiceTest extends TestCase implements Mailer { private $mailerCalls = 0; public function testMailer() { $sut = new Service($this); $sut->execute(); $this->assertEquals(2, $this->getCalls()); } public function send(Message $message) : void { $this->mailerCalls++; } }
37. Anonymous class Exploratory Single use Simple interface No side effects
38. class ServiceTest extends TestCase { public function testMailer() { $mailer = new class implements Mailer { private $calls = 0; public function send(Message $message) : void { $this->calls++; } puablic function getCalls() { return $this->calls; } }; $sut = new Service($mailer); $sut->execute(); $this->assertEquals(2, $mailer->getCalls()); } }
39. Hand made double Simple interfaces Simple behaviour Could need its
 own tests
40. Mocking library Large interfaces Complex behaviour Multiple scenarios
41. class ServiceTest extends TestCase { public function testMailer() { $mailer = $this->createMock(Mailer::class); $mailer->expects($this->once()) ->method(‘send’) ->with($this->isInstanceOf(Message::class)) ->willReturn(true); $sut = new Service($mailer); $sut->execute(); } }