def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def check_url_error_message(value):
    try:
        inputs.url(value)
        assert False, u"inputs.url({0}) should raise an exception".format(value)
    except ValueError as e:
        assert_equal(six.text_type(e),
                     (u"{0} is not a valid URL. Did you mean: http://{0}".format(value)))