phpunit ErrorException：尝试获取非对象的属性（Laravel / Entrust项目）

When I run phpunit on my Laravel based project I get an error: ErrorException: Trying to get property of non-object

But only on phpunit, the page renders fine.

This is the line of code in my blade template that is de cause of the error:

{{ $user->roles->first()->display_name }}

When I replace this with the following (ugly) code the phpunit tests run ok:

@php ($role = preg_replace('/[^a-z\d ]/i', '', $user->roles->pluck('display_name')) ) 
{{ $role }}

The roles are eager loaded in the controller:

$users->load('roles');

Any idea why phpunit throws this error (and laravel not) and how to sove this in a better way?