public void addChangeOfStateSubscription(Consumer<PlcValue> consumer, PlcSubscriptionHandle handle, PlcSubscriptionTag subscriptionTag) {
        LOGGER.debug("Adding change of state subscription: {}, {}, {}", consumer, handle, subscriptionTag);
        changeOfStateSubscriptions.put(handle, Pair.of((SimulatedTag) ((DefaultPlcSubscriptionTag) subscriptionTag).getTag(), consumer));
    }
Test device storing its state in memory.
Values are stored in a HashMap.
plc4j/drivers/simulated/src/main/java/org/apache/plc4x/java/simulated/connection/SimulatedDevice.java