How to share fixtures between tests in PHPUnit

I’m doing WordPress functional testing so I read the HTML and use Mastermind/HTML5 to transform the test. However, the tests now are getting slow because loading HTML document takes around 1s per test. I’d like to share the fixture between tests so I don’t have to do the parse for each test. But I have one constraint, the method that gets the html from is in the parent class which is non-static method

https://core.trac.wordpress.org/browser/trunk/tests/phpunit/includes/testcase.php?rev=32953#L328

What choice do I have to share the fixture between tests.

Here’s my example code

class Testcase extends WP_UnitTestCase {

    public function setUp() {
        parent::setUp();
    }

    public function get_dom( $path ) {
        $html = $this->go_to( $path ); // I cannot change this method
        // do some html parsing and return DOM
    }

}

Here’s my sample test

class Testcase1 extends Testcase {
     public setUp(){
          $this->dom = $this->get_dom('/')
     }
     public test_1() {
     }

     public test_2() {
     }
}

I was thinking of making the method get_dom static so it will just be called once but as far as I know static method cannot call non-static method. Am I correct? and if yes is there anyway I could share the fixture between tests?