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 test_bad_urls():
    values = [
        'foo',
        'http://',
        'http://example',
        'http://example.',
        'http://.com',
        'http://invalid-.com',
        'http://-invalid.com',
        'http://inv-.alid-.com',
        'http://inv-.-alid.com',
        'foo bar baz',
        u'foo \u2713',
        'http://@foo:bar@example.com',
        'http://:bar@example.com',
        'http://bar:bar:bar@example.com',
    ]

    for value in values:
        yield check_bad_url_raises, value