Upgrading PHPUnit from 4.8 to 5.5

You could create additional test class called TestAdapter which will extend PHPUnit_Framework_TestCase

class TestAdapter extends PHPUnit_Framework_TestCase
{
    /**
    * Override your deprecated method
    */
    public function getMock()
    {
        return $this->createMock();
    }
}

Then you just need to extend all of your tests from this class.