Era is a date & time library.
Testing datetime-based code is difficult if it's coupled to the system time. Suppose you have an age calculator:
<?php
class AgeCalculator
{
/**
* @param DateTime $from
* @return int
*/
public function age(DateTime $from)
{
$now = new DateTime;
return $from->diff($now)->y;
}
}And a test for it:
<?php
class AgeCalculatorTest extends PHPUnit_Framework_TestCase
{
public function testAge()
{
$ageCalculator = new AgeCalculator;
$birthdate = new DateTime('1987-05-31');
$this->assertEquals(25, $ageCalculator->age($birthdate));
}
}Now, the test is brittle because it will pass only between 2012-05-31 and 2013-05-30. After that, it'll start
failing.
To uncouple your code from the system time, you need an abstraction for it. Here comes Calendar:
<?php
use Elnur\Era\CalendarInterface;
class AgeCalculator
{
/**
* @var CalendarInterface
*/
private $calendar;
/**
* @var CalendarInterface $calendar
*/
public function __construct(CalendarInterface $calendar)
{
$this->calendar = $calendar;
}
/**
* @param DateTime $from
* @return int
*/
public function age(DateTime $from)
{
$now = $this->calendar->now();
return $from->diff($now)->y;
}
}Notice how we use a CalendarInterface instance to get the current datetime. Now, you can mock it to make the test
solid:
<?php
class AgeCalculatorTest extends PHPUnit_Framework_TestCase
{
public function testAge()
{
$now = new DateTime('2012-05-31');
$calendar = $this->getMockForAbstractClass('Elnur\Era\CalendarInterface');
$calendar
->expects($this->any())
->method('now')
->will($this->returnValue($now))
;
$ageCalculator = new AgeCalculator($calendar);
$birthdate = new DateTime('1987-05-31');
$this->assertEquals(25, $ageCalculator->age($birthdate));
}
}Now, the test won't fail just because some time have passed.
And here's how you use your new shiny AgeCalculator:
<?php
$calendar = new Calendar;
$ageCalculator = new AgeCalculator($calendar);
$birthdate = new DateTime('1987-05-31');
$age = $ageCalculator->age($birthdate);AgeCalculator is the class implemented above but with a tweak: if you ask it to figure out the age of something from
the future, it returns 0.
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