assertThrows(IllegalArgumentException.class, () -> new SimpleCircuitBreaker("invalid", 3, 2, -1));
    }

    @Test
    @DisplayName("Test statistics toString")
    void testStatisticsToString() throws Exception {
        circuitBreaker.call(() -> "success");

        SimpleCircuitBreaker.Statistics stats = circuitBreaker.getStatistics();
        String str = stats.toString();