import warnings

__unittest=True

class _AssertWarnsContext(object):
    def __init__(self, warningtype, testcase, msg=''):
        self.warningtype = warningtype
        warnings.filterwarnings('error')
        self.failureException = testcase.failureException

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, tb):
        if exc_type is None:
            try:
                exc_name = self.warningtype.__name__
            except AttributeError:
                exc_name = str(self.warningtype)
            raise self.failureException(
                "{0} not raised".format(exc_name))

        if not issubclass(exc_type, self.warningtype):
            raise self.failureException('"%s" does not match "%s"' %
                    (self.warningtype.__name__, str(exc_type.__name__)))

        return True

class CatchWarningsMixin(object):
    def assertWarns(self, wrnClass, callableObj=None, *args, **kwargs):
        context = _AssertWarnsContext(wrnClass, self)
        if callableObj is None:
            return context
        with context:
            callableObj(*args, **kwargs)