def METHOD_NAME(self, suite, source):
    default = os.path.isfile
    verifier = {'Root': lambda source: source == '',
                'Subsuites': os.path.isdir}.get(suite, default)
    if (source and not os.path.isabs(source)) or not verifier(source):
        raise AssertionError("Suite '%s' has wrong source '%s'."
                             % (suite, source))