From 9efdd40d1f965428cf0974105f6ff5199e99c5a5 Mon Sep 17 00:00:00 2001
From: Douwe Maan <hi@douwe.me>
Date: Fri, 24 Oct 2025 22:06:53 +0000
Subject: [PATCH] Ensure ToolCallPart resulting from
 TestModel(custom_output_args=...) always holds a dict

---
 pydantic_ai_slim/pydantic_ai/models/test.py |   9 +-
 tests/models/test_model_test.py             | 102 ++++++++++++++++++++
 2 files changed, 108 insertions(+), 3 deletions(-)

diff --git a/pydantic_ai_slim/pydantic_ai/models/test.py b/pydantic_ai_slim/pydantic_ai/models/test.py
index 6b772365ba..170113a999 100644
--- a/pydantic_ai_slim/pydantic_ai/models/test.py
+++ b/pydantic_ai_slim/pydantic_ai/models/test.py
@@ -44,11 +44,14 @@ class _WrappedTextOutput:
     value: str | None
 
 
-@dataclass
+@dataclass(init=False)
 class _WrappedToolOutput:
     """A wrapper class to tag an output that came from the custom_output_args field."""
 
-    value: Any | None
+    value: dict[str, Any] | None
+
+    def __init__(self, value: Any | None):
+        self.value = pydantic_core.to_jsonable_python(value)
 
 
 @dataclass(init=False)
@@ -364,7 +367,7 @@ def __init__(self, schema: _utils.ObjectJsonSchema, seed: int = 0):
         self.defs = schema.get('$defs', {})
         self.seed = seed
 
-    def generate(self) -> Any:
+    def generate(self) -> dict[str, Any]:
         """Generate data for the JSON schema."""
         return self._gen_any(self.schema)
 
diff --git a/tests/models/test_model_test.py b/tests/models/test_model_test.py
index d73e8579c3..f6b4af74b1 100644
--- a/tests/models/test_model_test.py
+++ b/tests/models/test_model_test.py
@@ -69,6 +69,40 @@ def test_custom_output_args():
     agent = Agent(output_type=tuple[str, str])
     result = agent.run_sync('x', model=TestModel(custom_output_args=['a', 'b']))
     assert result.output == ('a', 'b')
+    assert result.all_messages() == snapshot(
+        [
+            ModelRequest(
+                parts=[
+                    UserPromptPart(
+                        content='x',
+                        timestamp=IsNow(tz=timezone.utc),
+                    )
+                ]
+            ),
+            ModelResponse(
+                parts=[
+                    ToolCallPart(
+                        tool_name='final_result',
+                        args={'response': ['a', 'b']},
+                        tool_call_id='pyd_ai_tool_call_id__final_result',
+                    )
+                ],
+                usage=RequestUsage(input_tokens=51, output_tokens=7),
+                model_name='test',
+                timestamp=IsNow(tz=timezone.utc),
+            ),
+            ModelRequest(
+                parts=[
+                    ToolReturnPart(
+                        tool_name='final_result',
+                        content='Final result processed.',
+                        tool_call_id='pyd_ai_tool_call_id__final_result',
+                        timestamp=IsNow(tz=timezone.utc),
+                    )
+                ]
+            ),
+        ]
+    )
 
 
 def test_custom_output_args_model():
@@ -79,12 +113,80 @@ class Foo(BaseModel):
     agent = Agent(output_type=Foo)
     result = agent.run_sync('x', model=TestModel(custom_output_args={'foo': 'a', 'bar': 1}))
     assert result.output == Foo(foo='a', bar=1)
+    assert result.all_messages() == snapshot(
+        [
+            ModelRequest(
+                parts=[
+                    UserPromptPart(
+                        content='x',
+                        timestamp=IsNow(tz=timezone.utc),
+                    )
+                ]
+            ),
+            ModelResponse(
+                parts=[
+                    ToolCallPart(
+                        tool_name='final_result',
+                        args={'foo': 'a', 'bar': 1},
+                        tool_call_id='pyd_ai_tool_call_id__final_result',
+                    )
+                ],
+                usage=RequestUsage(input_tokens=51, output_tokens=6),
+                model_name='test',
+                timestamp=IsNow(tz=timezone.utc),
+            ),
+            ModelRequest(
+                parts=[
+                    ToolReturnPart(
+                        tool_name='final_result',
+                        content='Final result processed.',
+                        tool_call_id='pyd_ai_tool_call_id__final_result',
+                        timestamp=IsNow(tz=timezone.utc),
+                    )
+                ]
+            ),
+        ]
+    )
 
 
 def test_output_type():
     agent = Agent(output_type=tuple[str, str])
     result = agent.run_sync('x', model=TestModel())
     assert result.output == ('a', 'a')
+    assert result.all_messages() == snapshot(
+        [
+            ModelRequest(
+                parts=[
+                    UserPromptPart(
+                        content='x',
+                        timestamp=IsNow(tz=timezone.utc),
+                    )
+                ]
+            ),
+            ModelResponse(
+                parts=[
+                    ToolCallPart(
+                        tool_name='final_result',
+                        args={'response': ['a', 'a']},
+                        tool_call_id='pyd_ai_tool_call_id__final_result',
+                    )
+                ],
+                usage=RequestUsage(input_tokens=51, output_tokens=7),
+                model_name='test',
+                timestamp=IsNow(tz=timezone.utc),
+            ),
+            ModelRequest(
+                parts=[
+                    ToolReturnPart(
+                        tool_name='final_result',
+                        content='Final result processed.',
+                        tool_call_id='pyd_ai_tool_call_id__final_result',
+                        timestamp=IsNow(tz=timezone.utc),
+                    )
+                ]
+            ),
+        ]
+    )
 
 
 def test_tool_retry():