feat(pyamber): validate executor definitions

amber/src/main/python/core/architecture/managers/executor_manager.py

@@ -125,7 +125,8 @@ def load_executor_definition(self, code: str) -> type(Operator):
         executors = list(
             filter(self.is_concrete_operator, executor_module.__dict__.values())
         )
-        assert len(executors) == 1, "There should be one and only one Operator defined"
+        if len(executors) != 1:
+            raise ValueError("There should be one and only one Operator defined")
         return executors[0]
 
     def close(self) -> None:

amber/src/test/python/core/architecture/managers/test_executor_manager.py

@@ -407,17 +407,15 @@ def test_update_with_source_mismatch_raises_assertion(self, initialized_manager)
             )
         assert "SourceOperator API" in str(exc_info.value)
 
-    def test_update_with_no_operator_class_raises_assertion(self, initialized_manager):
-        # load_executor_definition asserts exactly one Operator subclass exists
-        # in the module — an empty module trips that assertion.
-        with pytest.raises(AssertionError) as exc_info:
+    def test_update_with_no_operator_class_is_rejected(self, initialized_manager):
+        with pytest.raises(ValueError) as exc_info:
             initialized_manager.update_executor(code=NO_OPERATOR_CODE, is_source=False)
         assert "one and only one Operator" in str(exc_info.value)
 
-    def test_update_with_multiple_operator_classes_raises_assertion(
+    def test_update_with_multiple_operator_classes_is_rejected(
         self, initialized_manager
     ):
-        with pytest.raises(AssertionError) as exc_info:
+        with pytest.raises(ValueError) as exc_info:
             initialized_manager.update_executor(
                 code=TWO_OPERATORS_CODE, is_source=False
             )