If 'value' is non-null, that value is first set using the style attribute
// of the target element.
function verify_computed_type(name, value, expected) {
    if (expected == CSSUnparsedValue) {
        throw 'CSSUnparsedValue may not be used as expected type';
    }

    try {
        if (value != null) {
            target.style = `${name}: ${value}`;
        }

        let computedValue = target.computedStyleMap().get(name);

        assert_false(computedValue instanceof CSSUnparsedValue);
        assert