public static Long getHeartbeatIntervalMs() {
        String interval = SentinelConfig.getConfig(HEARTBEAT_INTERVAL_MS);
        try {
            return interval == null ? null : Long.parseLong(interval);
        } catch (Exception ex) {
            RecordLog.warn("[TransportConfig] Failed to parse heartbeat interval: " + interval);
            return null;
        }
    }
@Test
    public void testGetHeartbeatInterval() {
        long interval = 20000;
        assertNull(TransportConfig.getHeartbeatIntervalMs());
        // Set valid interval.
        SentinelConfig.setConfig(TransportConfig.HEARTBEAT_INTERVAL_MS, String.valueOf(interval));
        assertEquals(new Long(interval), TransportConfig.getHeartbeatIntervalMs());
        // Set invalid interval.
        SentinelConfig.setConfig(TransportConfig.HEARTBEAT_INTERVAL_MS, "Sentinel");
        assertNull(TransportConfig.getHeartbeatIntervalMs());
    }