Error when run unit test

[khanhnv-2091]

Hi, I run a unit test give an error

sun@labs:~/git/phortress$ vendor/bin/phpunit
PHPUnit 4.2.6 by Sebastian Bergmann.

Configuration read from /home/sun/git/phortress/phpunit.xml.dist

The Xdebug extension is not loaded. No code coverage will be generated.

PHP Fatal error:  Declaration of SebastianBergmann\Comparator\DOMNodeComparator::assertEquals($expected, $actual, $delta = 0, $canonicalize = false, $ignoreCase = false) must be compatible with SebastianBergmann\Comparator\ObjectComparator::assertEquals($expected, $actual, $delta = 0, $canonicalize = false, $ignoreCase = false, array &$processed = Array) in /home/sun/git/phortress/vendor/sebastian/comparator/src/DOMNodeComparator.php on line 149