       class="labelled"
        type="button"
        aria-labelledby="label4"
        data-expectedlabel="foo default bar"
        data-testname="aria-labelledby reference to element with default slotted text content and aria-label on slot"></button>

<script>

document.getElementById('host1').attachShadow({ mode: 'open' }).innerHTML = 'foo <slot></slot> bar';
document.getElementById('host2').attachShadow({ mode: 'open' }).innerHTML = 'foo <slot>default</slot> bar';
document.getElementById('host3').attachS