Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
<?php
/**
* This is the clock interface. It's really simple, you write it once, use it anywhere.
* Cool extra things you can do:
* - have it return custom value objects
* - separate method for currentDate() without time part
*/
interface Clock
{
public function currentTime(): DateTimeImmutable;
}
/**
* SystemClock just relies on the current system:
*
* Cool extra things you can do:
* - force a timezone regardless of the current system settings
* - settle disputes about DateTimeImmutable vs DateTime in your codebase ONCE AND FOR ALL, MWAHHAHA
*/
class SystemClock implements Clock
{
public function currentTime(): DateTimeImmutable
{
return new DateTimeImmutable('now');
}
}
/**
* Mock Clock just returns a date you set.
*
* Cool extra things you can do:
*
* - mock current time in unit tests
* - shortcut constructors like MockClock::isCurrently('10:41')
* - have a setter to advance the clock as the test progresses
*/
class MockClock implements Clock
{
private $fixedTime;
public function __construct(DateTimeImmutable $dateTime)
{
$this->fixedTime = $dateTime;
}
public function currentTime(): DateTimeImmutable
{
return $this->fixedTime;
}
}
// Okay, how/why would we use it? Okay, consider this off-the-cuff use case{
class DaysUntilBirthdayCalculator
{
/** @var Clock */
private $clock;
public function __construct(Clock $clock)
{
$this->clock = $clock;
}
public function daysLeft(DateTimeImmutable $myBirthday): int
{
$currentTime = $this->clock->currentTime();
if ($currentTime > $myBirthday) {
throw new LogicException("Hey, you already had that birthday!");
}
return (int)$myBirthday->diff($currentTime)->format("%a");
}
}
// Cool, number of days until my birthday!
$myBirthday = new DateTimeImmutable('Nov 10, 2016');
$calculator = new DaysUntilBirthdayCalculator(new SystemClock());
var_dump($calculator->daysLeft($myBirthday));
// Oh wait, I wrote a unit test for this last month but it constantly fails!
var_dump($calculator->daysLeft($myBirthday) === 34);
// No worries, let's use a mock clock. Now we can write unit tests that we can rely on always!
$calculator = new DaysUntilBirthdayCalculator(
new MockClock(new DateTimeImmutable('2016-10-18'))
);
var_dump($calculator->daysLeft($myBirthday) === 23);
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.