Default `init` plugin was not properly raising when called with an invalid optimization level (#12170)

* Raise instead of return.

---

Co-authored-by: Evgenii Zheltonozhskii <zheltonozhskiy@gmail.com>

* link

* reno

---------

Co-authored-by: Evgenii Zheltonozhskii <zheltonozhskiy@gmail.com>

qiskit/transpiler/preset_passmanagers/builtin_plugins.py

@@ -158,7 +158,7 @@ class DefaultInitPassManager(PassManagerStagePlugin):
             init.append(CommutativeCancellation())
 
         else:
-            return TranspilerError(f"Invalid optimization level {optimization_level}")
+            raise TranspilerError(f"Invalid optimization level {optimization_level}")
         return init
 
 

releasenotes/notes/followup_11468-61c6181e62531796.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    The default ``init`` plugin was not properly raising a :class:`.TranspilerError` when called with an invalid optimization level.

test/python/transpiler/test_stage_plugin.py

@@ -86,6 +86,15 @@ class TestStagePassManagerPlugin(QiskitTestCase):
         )
         self.assertIsInstance(pm, PassManager)
 
+    def test_init_invalid_optlevel(self):
+        """Test default init stage with invalid optimization level.
+        See: https://github.com/Qiskit/qiskit/pull/12170"""
+        plugin_manager = PassManagerStagePluginManager()
+        with self.assertRaises(TranspilerError):
+            plugin_manager.get_passmanager_stage(
+                "init", "default", PassManagerConfig(), optimization_level=4
+            )
+
 
 @ddt.ddt
 class TestBuiltinPlugins(QiskitTestCase):