PHPunit put data in global

I hope someone can help me with this. My problem is, that i'm trying to mock globals in phpunit or something like that. Just trying to get the d**m globals running.

This is my construct

$this->testclass = $this->getMockBuilder('myClass')
                ->disableOriginalConstructor()
                ->setMethods(array(
                   'test' //<==== just setting it here for fun
                ))
                ->getMock();

This is my unit test

public function testCheckuniqueName() {
    $this->testclass->ixtools = new GlobalModx(); //<---- trying to get the global
    $this->testclass->checkuniqueName('empty', ' Back_test', 'testitem', true);
}

new GlobalModx() is a class i created to set globals and other functions i want to mock

class GlobalModx {

    public $confDB;


    public function __construct() {

        $this->confDB = new \stdClass();
        $this->confDB->attributes = array();
    }



}

My php function i try to test

    public function checkuniqueName(){
            global $ixTools; //<--- this is the bastard
            $dbAttributes = $ixTools->confDB->attributes['attributes'][$company];

//somecode i can't show

            return true;
        }

As you can see i try to reset the global and give it data. But all i get is

testCheckuniqueName() Trying to get property of non-object

I need to get data in the global. But phpunit won't let me