Accessing a property in a child class which has been modified by a parent class method

I am working on an application and I have run into this dilemma. Below is a very simplified version but I am wondering if its possible

Example:

class A{

    public $test = null;

    public function method1(){
      $this->test = 'finished';
    }
}

class B extends A{

    public function getMethod1Test(){
      retu $this->test;
    }
}

$a = new A();
$a->method1();

$b = new B();
$b->getMethod1Test(); //this currently retus NULL

How can I modify this such that it retus the value 'finished' without reinserting the modified value into class B?

Thanks