SimpleCircuitBreaker.Statistics stats = circuitBreaker.getStatistics();
        assertEquals(1, stats.rejectedCalls);
    }

    @Test
    @DisplayName("Test fallback used when circuit is open")
    void testFallbackWhenOpen() throws Exception {
        // Open the circuit
        circuitBreaker.tripBreaker();

        String result = circuitBreaker.call(() -> "primary", () -> "fallback");