Ensure tuple for passed in arbiter addr

tests/test_spawning.py

@@ -1,6 +1,7 @@
 """
 Spawning basics
 """
+from typing import Dict, Tuple
 
 import pytest
 import trio
@@ -11,7 +12,11 @@ from conftest import tractor_test
 data_to_pass_down = {'doggy': 10, 'kitty': 4}
 
 
-async def spawn(is_arbiter, data, arb_addr):
+async def spawn(
+    is_arbiter: bool,
+    data: Dict,
+    arb_addr: Tuple[str, int],
+):
     namespaces = [__name__]
 
     await trio.sleep(0.1)

tractor/_root.py

@@ -95,10 +95,10 @@ async def open_root_actor(
             "Debug mode is only supported for the `trio` backend!"
         )
 
-    arbiter_addr = (host, port) = arbiter_addr or (
+    arbiter_addr = (host, port) = tuple(arbiter_addr or (
         _default_arbiter_host,
-        _default_arbiter_port
-    )
+        _default_arbiter_port,
+    ))
 
     loglevel = loglevel or log.get_loglevel()
     if loglevel is not None: