// Test successful heartbeat
        assertTrue(mockService.processHeartbeat(regId, 1));
        assertTrue(mockService.processHeartbeat(regId, 2));

        // Test heartbeat for non-existent registration
        assertFalse(mockService.processHeartbeat("non-existent", 1));

        // Clean up
        mockService.unregisterWitness(regId);
    }

    @Test

     *
     * @param registrationId the registration ID
     * @param sequenceNumber the sequence number
     * @return true if heartbeat was successful
     */
    public boolean processHeartbeat(String registrationId, long sequenceNumber) {
        MockRegistration registration = registrations.get(registrationId);
        if (registration != null) {