tests: Provide a meaningful error message

When the sigint subprocess raises a Python exception (e.g. due to
missing features), the process remains open indefinitely, which
causes the unit test to time out and the Python interpreter to
terminate while the subprocess pipe is still open.

testsuite/python/sigint.py

@@ -25,6 +25,12 @@
 import os
 
 
+EXPECTED_TRACEBACK_ENDING = """ in handle_sigint
+    signal.raise_signal(signal.Signals.SIGINT)
+KeyboardInterrupt
+"""
+
+
 class SigintTest(ut.TestCase):
 
     script = str(pathlib.Path(__file__).parent / 'sigint_child.py')
@@ -43,8 +49,8 @@ def check_signal_handling(self, process, sig):
             self.assertEqual(traceback, "")
         elif sig == signal.Signals.SIGINT:
             self.assertIn(" self.integrator.run(", traceback)
-            self.assertTrue(traceback.endswith(
-                " in handle_sigint\n    signal.raise_signal(signal.Signals.SIGINT)\nKeyboardInterrupt\n"))
+            self.assertTrue(traceback.endswith(EXPECTED_TRACEBACK_ENDING),
+                            msg=f"Traceback failed string match:\n{traceback}")
 
     def test_signal_handling(self):
         signals = [signal.Signals.SIGINT, signal.Signals.SIGTERM]