test: Avoid shutdown race in NetworkThread

test/functional/test_framework/test_framework.py

@@ -345,6 +345,7 @@ class BitcoinTestFramework(metaclass=BitcoinTestMetaClass):
         self.log.debug('Setting up network thread')
         self.network_thread = NetworkThread()
         self.network_thread.start()
+        self.wait_until(lambda: self.network_thread.network_event_loop.is_running())
 
         if self.options.usecli:
             if not self.supports_cli: