'Fails if the given ``item`` is not a Unicode string.
Use `Should Be Byte String` if you want to verify the ``item`` is a
byte string, or `Should Be String` if both Unicode and byte strings
are fine. See `Should Be String` for more details about Unicode
strings and byte strings.
The default error message can be overridden with the optional
``msg`` argument.'

def should_be_unicode_string(self, item, msg=None):

    if (not is_unicode(item)):
        self._fail(msg, "'%s'    is    not    a    Unicode    string.", item)
