public static Builder custom() {
        return new Builder();
    }
@Test
    public void builderTimeoutIsNegative() throws Exception {
        exception.expect(IllegalArgumentException.class);
        exception.expectMessage(TIMEOUT_DURATION_MUST_NOT_BE_NEGATIVE);
        RateLimiterConfig.custom()
            .timeoutDuration(Duration.ofNanos(-1));
    }