Add test for missing @workflow_run_operation decorator

tests/nexus/test_handler_interface_implementation.py

@@ -44,19 +44,39 @@ async def op(
     error_message = None
 
 
+class MissingWorkflowRunDecorator(_InterfaceImplementationTestCase):
+    """Missing @workflow_run_operation decorator raises appropriate error."""
+
+    @nexusrpc.service
+    class Interface:
+        my_workflow_op: nexusrpc.Operation[str, int]
+
+    class Impl:
+        # Method exists but MISSING @workflow_run_operation decorator
+        async def my_workflow_op(
+            self, _ctx: WorkflowRunOperationContext, _input: str
+        ) -> nexus.WorkflowHandle[int]:
+            raise NotImplementedError
+
+    error_message = "does not implement an operation with method name 'my_workflow_op'"
+
+
 @pytest.mark.parametrize(
     "test_case",
     [
         ValidImpl,
         ValidWorkflowRunImpl,
+        MissingWorkflowRunDecorator,
     ],
 )
 def test_service_decorator_enforces_interface_conformance(
     test_case: type[_InterfaceImplementationTestCase],
 ):
     if test_case.error_message:
         with pytest.raises(Exception) as ei:
-            nexusrpc.handler.service_handler(test_case.Interface)(test_case.Impl)
+            nexusrpc.handler.service_handler(service=test_case.Interface)(
+                test_case.Impl
+            )
         err = ei.value
         assert test_case.error_message in str(err)
     else:

tests/nexus/test_workflow_caller.py

@@ -1301,9 +1301,6 @@ async def run(
         return await nexus_client.execute_operation(service_cls.op, None)  # type: ignore
 
 
-# TODO(nexus-prerelease): check missing decorator behavior
-
-
 async def test_service_interface_and_implementation_names(
     client: Client, env: WorkflowEnvironment
 ):