A comparator object for PHPUnit to support asserting that two DateTime objects are logically equaly.

DateTimeComparator.php

<?php
/**
 * Class DateTimeComparator
 *
 * Custom Comparator for PHPUnit to compare two DateTime objects
 * The default object comparator will report some DateTime object pairs
 * as not equal even if they are canonically equal because the object
 * comparator looks a exact object field values.  A DateTime object
 * can have multiple timezone values that represent the same timezone
 * however.  This comparator compares the object's UTC timestamps
 *
 */
class DateTimeComparator extends \PHPUnit_Framework_Comparator
{

    /**
     * Returns whether the comparator can compare two values.
     *
     * @param  mixed $expected The first value to compare
     * @param  mixed $actual The second value to compare
     * @return boolean
     */
    public function accepts($expected, $actual)
    {
       return $expected instanceof \DateTime && $actual instanceof \DateTime;
    }

    /**
     * Asserts that two values are equal.
     *
     * @param  DateTime $expected The first value to compare
     * @param  DateTime $actual The second value to compare
     * @param float|int $delta The allowed numerical distance between two values to
     *                      consider them equal
     * @param  bool $canonicalize If set to TRUE, arrays are sorted before
     *                             comparison
     * @param  bool $ignoreCase If set to TRUE, upper- and lowercasing is
     *                           ignored when comparing string values
     * @throws \PHPUnit_Framework_ComparisonFailure Thrown when the comparison
     *                           fails. Contains information about the
     *                           specific errors that lead to the failure.
     */
    public function assertEquals($expected, $actual, $delta = 0, $canonicalize = FALSE, $ignoreCase = FALSE)
    {
        /* @var $expected \DateTime */
        /* @var $actual \DateTime */
        if (abs($expected->getTimestamp() - $actual->getTimestamp()) > $delta)
        {
            throw new PHPUnit_Framework_ComparisonFailure(
                $expected,
                $actual,
                $expected->format(\DateTime::ISO8601),
                $actual->format(\DateTime::ISO8601)
            );
        }
    }
}

example.php

//register the comparator with PHPUnit.
//This is typically done in your bootstrap file
PHPUnit_Framework_ComparatorFactory::getDefaultInstance()->register(new DateTimeComparator());



//in a test...
$date1 = new DateTime('2013-01-01 00:00:00', new DateTimeZone('UTC));
$date2 = new DateTime('2012-12-31 19:00:00', new DateTimeZone('America/New_York')); //assuming current DST offest is UTC - 5hrs


$this->assertEquals($date1, $date2);

Version for phpunit 7+ (requires php7):

<?php

namespace TESTS;

use SebastianBergmann\Comparator\Comparator;
use SebastianBergmann\Comparator\ComparisonFailure;

class DateTimeComparator extends Comparator
{
	public function accepts($expected, $actual)
	{
		return $expected instanceof \DateTimeInterface && $actual instanceof \DateTimeInterface;
	}

	public function assertEquals($expected, $actual, $delta = 0, $canonicalize = FALSE, $ignoreCase = FALSE)
	{
		if (abs($expected->getTimestamp() - $actual->getTimestamp()) > $delta) {
			throw new ComparisonFailure(
				$expected,
				$actual,
				$expected->format(\DateTime::ISO8601),
				$actual->format(\DateTime::ISO8601)
			);
		}
	}
}

Comments omitted on purpose.