How to test error handling functions in Javascript

I m trying to write unit test cases to handle error codes that are defined below. not sure how to achieve it.

module.exports = {
    Error: Err,
    BadRequest: function () {
        return new Err(400, 'Bad Request');
    },
    NotAcceptable: function () {
        return new Err(406, 'Not Acceptable');
    },
    NotAuthorized: function () {
        return new Err(401, 'Not Authorized');
    }
};

function Err(code, message) {
    assert(code, 'code');

    Error.call(this);
    Error.captureStackTrace(this, this.constructor);

    Object.defineProperty(this, 'code', {
        enumerable: true,
        value: code
    });

    this.reason = message;
}