The snippet as you posted it should not cause an error. Is there anything else to this test class? It looks like maybe the TestCase class you're extending has a problem. Does your app generally work except for this test?
Actually, it's probably because you're naming your method setUp. Call parent::setUp() in your setUp method, or better, dont call it setUp(). Instead, use an annotation to make sure it gets run before your test.
Thank you corbosman! After reading your comment, I had a look at the parent TestCase and saw that it contained a createApplication() method. I put that before the Limelight instantiation and it works now.
public function setUp()
{
$this->createApplication();
$limelight = new Limelight();
}
``