Explicitly stop the test watchdog at exit.

tests/watchdog/__init__.py

@@ -13,6 +13,7 @@
 
 __all__  = ["start", "register_spawn", "unregister_spawn"]
 
+import atexit
 import os
 import sys
 import psutil
@@ -43,6 +44,13 @@ def start():
 
     _stream = messaging.JsonIOStream(_process.stdout, _process.stdin, watchdog_name)
     assert _stream.read_json() == "ready"
+    atexit.register(stop)
+
+
+def stop():
+    if _stream is None:
+        return
+    _stream.write_json(["stop"])
 
 
 def register_spawn(pid, name):

tests/watchdog/worker.py

@@ -45,10 +45,17 @@ def main(tests_pid):
             except Exception:
                 break
 
-            command, pid, name = message
-            pid = int(pid)
+            command = message[0]
+            args = message[1:]
+
+            if command == "stop":
+                assert not args
+                break
+
+            elif command == "register_spawn":
+                pid, name = args
+                pid = int(pid)
 
-            if command == "register_spawn":
                 log.debug(
                     "watchdog-{0} registering spawned process {1} (pid={2})",
                     tests_pid,
@@ -59,6 +66,9 @@ def main(tests_pid):
                 spawned_processes[pid] = psutil.Process(pid)
 
             elif command == "unregister_spawn":
+                pid, name = args
+                pid = int(pid)
+
                 log.debug(
                     "watchdog-{0} unregistering spawned process {1} (pid={2})",
                     tests_pid,