feat: isRegistered method on IBus

src/main/java/ftbsc/geb/GEB.java

@@ -63,6 +63,12 @@ public void unregisterListener(IListener listener) {
 		);
 	}
 
+	@Override
+	public boolean isRegistered(IListener listener) {
+		Set<IListener> listeners = this.listenerMap.get(listener.getClass());
+		return listeners != null && listeners.contains(listener);
+	}
+
 	/**
 	 * Dispatches an event, calling all of its listeners that are subscribed to this bus.
 	 * @param event the event to fire

src/main/java/ftbsc/geb/api/IBus.java

@@ -13,11 +13,18 @@ public interface IBus {
 	void registerListener(IListener listener);
 
 	/**
-	 * Unregister a listener from the bus.
+	 * Unregisters a listener from the bus.
 	 * @param listener the listener
 	 */
 	void unregisterListener(IListener listener);
 
+	/**
+	 * Tells you whether a listener is currently registered.
+	 * Ideally this should be efficient.
+	 * @return true if the listener is registered
+	 */
+	boolean isRegistered(IListener listener);
+
 	/**
 	 * Dispatches an event, calling all of its listeners that are subscribed to this bus.
 	 * @param event the event to fire