ection").moveBefore(element, null);
        await Promise.resolve();
        assert_array_equals(reactions, ["disconnected", "connected"]);
    }, "the disconnected/connected callbacks should be called when no other callback is defined");

    promise_test(async t => {
        const ce = document.getElementById("ce");
        let reactions = [];
        const element_name = unique_element_name();
        customElements.define(element_name,
            class MockCustomElement extends HTMLElement {
          