tests: Warn about processes which don't exit cleanly

pytest.ini

@@ -81,4 +81,5 @@ filterwarnings =
     error
     # See https://github.com/HypothesisWorks/hypothesis/issues/2370
     ignore:.*which is reset between function calls but not between test cases generated by:hypothesis.errors.HypothesisDeprecationWarning
+    default:Test process .* failed to terminate!:UserWarning
 faulthandler_timeout = 90

tests/end2end/fixtures/testprocess.py

@@ -22,6 +22,7 @@
 import re
 import os
 import time
+import warnings
 
 import attr
 import pytest
@@ -316,8 +317,11 @@ class Process(QObject):
         else:
             self.proc.terminate()
 
-        ok = self.proc.waitForFinished()
+        ok = self.proc.waitForFinished(5000)
         if not ok:
+            cmdline = ' '.join([self.proc.program()] + self.proc.arguments())
+            warnings.warn(f"Test process {cmdline} with PID {self.proc.processId()} "
+                          "failed to terminate!")
             self.proc.kill()
             self.proc.waitForFinished()