I cant retrieve var from parent class:

class core {
    var $variable;
    var $test;

    function __construct() {}

    public function setVar($var) 
        $this->variable = $var;
    }
}

class test extends core {
    public function getVar() {
        return $this->variable;
        //also if i echo here i can't see !!!!
    }
}

$core = new core();
$core->test = new test();
print $core->test->getVar();

Any help??