I'm using atoum for our application testing, it relies on xdebug to produce its code coverage.
I've noticed than covarage is a bit lower using PHP 7 than PHP 5.6 (both with xdebug 2.4.0beta1 - all PHP packages from Remi's repository on my Fedora box).

Sounds like difference is on some syntax like:

$builder->add(
'build_age',
'choice',
array([...])
);

On PHP 5.6, all code is considered as covered, on PHP 7, the build_age and choice lines are considered as not covered.

So all tests are running fine, but our global coverage amount is just lower, it's a bit disconcerting.

Details about PHP and XDebug versions:
$ php -v
PHP 5.6.15 (cli) (built: Oct 29 2015 14:56:28)
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2015 Zend Technologies
with Xdebug v2.4.0beta1, Copyright (c) 2002-2015, by Derick Rethans
$ php70 -v
PHP 7.0.0RC6 (cli) (built: Oct 28 2015 09:27:16) ( NTS )
Copyright (c) 1997-2015 The PHP Group
Zend Engine v3.0.0-dev, Copyright (c) 1998-2015 Zend Technologies
with Xdebug v2.4.0beta1, Copyright (c) 2002-2015, by Derick Rethans