Returns an error string if any of the dependencies failed

def dependency_failed(test, results):
        """Returns an error string if any of the dependencies failed"""
        for d in (NoseDepUtils.test_name(i) for i in dependencies[test]):
            if results.get(d) and results.get(d) != 'passed':
                return "Required test '{}' {}".format(d, results.get(d).upper())
        return None