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_unions(self):
        for code, tp in self.formats.items():
            class X(Union):
                _fields_ = [("x", c_char),
                            ("y", tp)]
            self.assertEqual((sizeof(X), code),
                                 (calcsize("%c" % (code)), code))