Issue #107: Stop attaching the child watcher multiple times

buildstream/_scheduler/job.py

@@ -114,7 +114,6 @@ class Job():
 
         # Wait for it to complete
         self.watcher = asyncio.get_child_watcher()
-        self.watcher.attach_loop(self.scheduler.loop)
         self.watcher.add_child_handler(self.pid, self.child_complete, self.element)
 
     # shutdown()

buildstream/_scheduler/scheduler.py

@@ -112,7 +112,10 @@ class Scheduler():
         for queue in queues:
             queue.attach(self)
 
+        # Ensure that we have a fresh new event loop, in case we want
+        # to run another test in this thread.
         self.loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(self.loop)
 
         # Add timeouts
         if self.ticker_callback: