 this.elementInternals = this.attachInternals();
      }
    });

    test(function(t) {
        t.add_cleanup(() => { myCE.elementInternals.states.delete('--green') });
        t.add_cleanup(() => { myCE2.elementInternals.states.delete('--green') });
        assert_false(myCE.elementInternals.states.has('--green'));
        assert_equals(getComputedStyle(myCE).getPropertyValue('color'), 'rgb(255, 0, 0)');
        assert_equals(getComputedStyle(myCE2).getPropertyValue('color'), 'rgb(255, 0, 0)');
        as