Error on constructing start operation with invalid conflict policy

Author: dandavison

temporalio/client.py

@@ -2606,6 +2606,8 @@ def __init__(
         name, result_type_from_run_fn = (
             temporalio.workflow._Definition.get_name_and_result_type(workflow)
         )
+        if id_conflict_policy == temporalio.common.WorkflowIDConflictPolicy.UNSPECIFIED:
+            raise ValueError("WorkflowIDConflictPolicy is required")
 
         self._start_workflow_input = UpdateWithStartStartWorkflowInput(
             workflow=name,

tests/worker/test_update_with_start.py

@@ -496,3 +496,22 @@ async def test_update_with_start_client_outbound_interceptor(
 
         wf_handle = await start_op.workflow_handle()
         assert await wf_handle.result() == "intercepted-workflow-arg"
+
+
+def test_with_start_workflow_operation_requires_conflict_policy():
+    with pytest.raises(ValueError):
+        WithStartWorkflowOperation(
+            WorkflowForUpdateWithStartTest.run,
+            0,
+            id="wid-1",
+            id_conflict_policy=WorkflowIDConflictPolicy.UNSPECIFIED,
+            task_queue="test-queue",
+        )
+
+    with pytest.raises(TypeError):
+        WithStartWorkflowOperation(  # type: ignore
+            WorkflowForUpdateWithStartTest.run,
+            0,
+            id="wid-1",
+            task_queue="test-queue",
+        )