feat: boolean function to check if world is broken (#66)

A broken world exception is raised for collective operations such as
send and recv. However, if those operations are not called and
runtime error is not raised, the broken world won't be noticed until
any of the operations is called. To check if the world is broken or not
without calling the operations, a new function is introduced.

multiworld/world_communicator.py

@@ -76,18 +76,32 @@ def __del__(self):
         """Cleanup the class instance."""
         del self._broken_world
 
-    def add_world(self, world_name):
+    def add_world(self, world_name) -> None:
         """Add a new world to the world comm manager."""
         self._broken_world[world_name] = False
 
-    def remove_world(self, world_name):
+    def remove_world(self, world_name) -> None:
         """Remove a world from the world comm manager."""
         logger.debug(f"remove world {world_name}")
         try:
             self._broken_world[world_name] = True
         except KeyError:
             pass
 
+    def is_broken(self, world_name: str) -> bool:
+        """Return true if the given world is broken; otherwise return false.
+
+        A world is considered broken if no key for the world name is found.
+
+        Args:
+            world_name: name of world
+
+        Returns:
+            A boolean value to indicate whether a world is broken or not.
+        """
+        logger.debug(f"check if world {world_name} is broken")
+        return self._broken_world.get(world_name, True)
+
     async def _wait_work(self, work: Work, world_name: str) -> None:
         """Do busy-waiting for work to be done.