Check the exit code.

tests/helpers/editor.py

@@ -272,6 +272,10 @@ class DebugAdapter(Closeable):
             self._output = self._proc.stdout.read()
             return self._output
 
+    @property
+    def returncode(self):
+        return self._proc.returncode
+
     def attach(self, **kwargs):
         if self._session is not None:
             raise RuntimeError('already attached')

tests/system_tests/test_main.py

@@ -119,5 +119,7 @@ class LifecycleTests(TestsBase, unittest.TestCase):
             lifecycle_handshake(session, 'launch')
             adapter.wait()
         out = adapter.output.decode('utf-8')
+        rc = adapter.returncode
 
         self.assertIn('done', out.splitlines())
+        self.assertEqual(rc, 0)