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TDD 101
6. Test doubles: the motion picture
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Test doubles:
the motion picture
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The plot
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You want to test an object that uses collaborators…
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You need to isolate its behaviour from that of its collaborators
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Then, you’ll need…
test doubles
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The argument
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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
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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
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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)
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The cast
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Dummy
No behavior
Only interface
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namespace Dojo\HappyBirthday\Logger;
interface SimpleLogger
{
public function log(string $channel, string $message): void;
}
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namespace Tests\Dojo\HappyBirthday\Double;
use Dojo\HappyBirthday\Logger\SimpleLogger;
class LoggerDummy implements SimpleLogger
{
public function log(string $channel, string $message): void
{
}
}
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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('[email protected]'),
new Customer('[email protected]'),
new Customer('[email protected]')
]);
$sendGreetings = new SendGreetings(
$clockService,
$customerRepository,
$mailer,
$logger
);
$sendGreetings->execute();
$this->assertEquals(3. $mailer->getMessagesSent());
}
}
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Stub
Programmed behavior
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namespace Dojo\HappyBirthday\Clock;
use DateTimeImmutable;
interface ClockService
{
public function currentDate(): DateTimeImmutable;
}
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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;
}
}
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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('[email protected]'),
new Customer('[email protected]'),
new Customer('[email protected]')
]);
$sendGreetings = new SendGreetings(
$clockService,
$customerRepository,
$mailer,
$logger
);
$sendGreetings->execute();
$this->assertEquals(3. $mailer->getMessagesSent());
}
}
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Fake
Behavior
implementation…
but best suited for
testing
Needs its own tests
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namespace Dojo\HappyBirthday\Contacts;
interface ContactRepositoryInterface
{
public function retrieveById(UUid $uuid): Contact;
}
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namespace Dojo\HappyBirthday\Contacts;
class InMemoryContactRepository implements ContactRepository
{
public function retrieveById(UUid $uuid): Contact
{
}
}
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Spy
Registers how is used
Fragility (coupling)
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interface Mailer
{
public function send(Message $message) : void;
}
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class MailerSpy implements Mailer
{
private $calls = 0;
public function send(Message $message) : void
{
$this->calls++;
}
public function getCalls()
{
return $this->calls;
}
}
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Mock
Has expectations
about how is used
Takes assertions
away from the test
Fragility (coupling)
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Taxonomy
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Behavior
Knowledge
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test doubles by behavior
dummy stub fake
no behavior fixed complete
Applies to any kind of double by knowledge
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test doubles by knowledge
passive spy mock
Applies to any kind of double by behavior
knows
nothing
registers
use
has
expectations
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How to
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i
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Design principles
Dem
SRP
OCP DIP
ISP
LSP
DRY Yagni
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The “real” object
Should have:
• No behavior
• No side effects
• Immutability
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Self-shunt Exploratory and sparse use
Simple interface
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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++;
}
}
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Anonymous
class
Exploratory
Single use
Simple interface
No side effects
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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());
}
}
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Hand made
double
Simple interfaces
Simple behaviour
Could need its
own tests
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Mocking
library
Large interfaces
Complex behaviour
Multiple scenarios
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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();
}
}
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