try {
    var foo = true;
    assert(foo.valueOf() === true);
    assert(true.valueOf() === true);

    assert(Boolean.prototype.valueOf.call(true) === true);
    assert(Boolean.prototype.valueOf.call(false) === false);

    let error = null;
    try {
        Boolean.prototype.valueOf.call("foo");
    } catch (err) {
        error = err;
    }

    assert(error instanceof Error);
    assert(error.name === "TypeError");
    assert(error.message === "Not a Boolean");

    console.log("PASS");
} catch (err) {
    console.log("FAIL: " + err);
}