nextElementSibling incorrect');
    assert.equal(after.previousElementSibling, child, 'previousElementSibling incorrect');
    assert.equal(child.previousElementSibling, before, 'previousElementSibling incorrect');
  });

  test('node accessors (empty logical tree)', function() {
    var element = document.createElement('x-simple');
    assert.equal(element.parentNode, null, 'parentNode incorrect');
    assert.equal(element.firstChild, null, 'firstChild incorrect');
    assert.equal(element.lastChild, null,