Pydantic Ai Testing

Testing PydanticAI Agents

TestModel (Deterministic Testing)

Use TestModel for tests without API calls:

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

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)