pydantic-ai-testing

# Testing PydanticAI Agents

## TestModel (Deterministic Testing)

Use `TestModel` for tests without API calls:

```python
import pytest
from pydantic_ai import Agent
from pydantic_ai.models.test import TestModel

def test_agent_basic():
    agent = Agent('openai:gpt-4o')

    # Override with TestModel for testing
    result = agent.run_sync('Hello', model=TestModel())

    # TestModel generates deterministic output based on output_type
    assert isinstance(result.output, str)
```

## TestModel Configuration

```python
from pydantic_ai.models.test import TestModel

# Custom text output
model = TestModel(custom_output_text='Custom response')
result = agent.run_sync('Hello', model=model)
assert result.output == 'Custom response'

# Custom structured output (for output_type agents)
from pydantic import BaseModel

class Response(BaseModel):
    message: str
    score: int

agent = Agent('openai:gpt-4o', output_type=Response)
model = TestModel(custom_output_args={'message': 'Test', 'score': 42})
result = agent.run_sync('Hello', model=model)
assert result.output.message == 'Test'

# Seed for reproducible random output
model = TestModel(seed=42)

# Force tool calls
model = TestModel(call_tools=['my_tool', 'another_tool'])
```

## Override Context Manager

```python
from pydantic_ai import Agent
from pydantic_ai.models.test import TestModel

agent = Agent('openai:gpt-4o', deps_type=MyDeps)

def test_with_override():
    mock_deps = MyDeps(db=MockDB())

    with agent.override(model=TestModel(), deps=mock_deps):
        # All runs use TestModel and mock_deps
        result = agent.run_sync('Hello')
        assert result.output
```

## FunctionModel (Custom Logic)

For complete control over model responses:

```python
from pydantic_ai import Agent, ModelMessage, ModelResponse, TextPart
from pydantic_ai.models.function import AgentInfo, FunctionModel

def custom_model(
    messages: list[ModelMessage],
    info: AgentInfo
) -> ModelResponse:
    """Custom model that inspects