diff --git a/tests/operation/parallel_test.py b/tests/operation/parallel_test.py
index 15a8346..1922207 100644
--- a/tests/operation/parallel_test.py
+++ b/tests/operation/parallel_test.py
@@ -2,6 +2,8 @@
 
 import importlib
 import json
+from collections.abc import Mapping
+from typing import Any
 from unittest.mock import Mock, patch
 
 import pytest
@@ -52,6 +54,11 @@ def create_test_context(
     )
 
 
+def _mock_call_kwargs_by_operation_id(mock: Mock) -> dict[str, Mapping[str, Any]]:
+    """Return mock call keyword arguments keyed by operation_id."""
+    return {call.kwargs["operation_id"]: call.kwargs for call in mock.call_args_list}
+
+
 def test_parallel_executor_init():
     """Test ParallelExecutor initialization."""
     executables = [Executable(index=0, func=lambda x: x)]
@@ -825,12 +832,12 @@ def create_id(self, i):
         )
 
     expected = item_serdes or batch_serdes
-    assert mock_serialize.call_args_list[0][1]["serdes"] is expected
-    assert mock_serialize.call_args_list[0][1]["operation_id"] == "child-0"
-    assert mock_serialize.call_args_list[1][1]["serdes"] is expected
-    assert mock_serialize.call_args_list[1][1]["operation_id"] == "child-1"
-    assert mock_serialize.call_args_list[2][1]["serdes"] is batch_serdes
-    assert mock_serialize.call_args_list[2][1]["operation_id"] == "parent"
+    calls_by_operation_id = _mock_call_kwargs_by_operation_id(mock_serialize)
+
+    assert set(calls_by_operation_id) == {"child-0", "child-1", "parent"}
+    assert calls_by_operation_id["child-0"]["serdes"] is expected
+    assert calls_by_operation_id["child-1"]["serdes"] is expected
+    assert calls_by_operation_id["parent"]["serdes"] is batch_serdes
 
 
 @pytest.mark.parametrize(
@@ -886,10 +893,11 @@ def create_id(self, i):
         )
 
     expected = item_serdes or batch_serdes
-    assert mock_deserialize.call_args_list[0][1]["serdes"] is expected
-    assert mock_deserialize.call_args_list[0][1]["operation_id"] == "child-0"
-    assert mock_deserialize.call_args_list[1][1]["serdes"] is expected
-    assert mock_deserialize.call_args_list[1][1]["operation_id"] == "child-1"
+    calls_by_operation_id = _mock_call_kwargs_by_operation_id(mock_deserialize)
+
+    assert set(calls_by_operation_id) == {"child-0", "child-1"}
+    assert calls_by_operation_id["child-0"]["serdes"] is expected
+    assert calls_by_operation_id["child-1"]["serdes"] is expected
 
 
 def test_parallel_result_serialization_roundtrip():