Pytest Testing Patterns

Pytest Testing Patterns for Constitutional AI

When to Apply

Automatically activate when:

• Creating new test files
• Modifying existing tests
• Debugging test failures
• Writing test fixtures or mocks

Project Testing Conventions

Test File Structure

Naming convention:

tests/test_{module}.py  # Matches source: constitutional_ai/{module}.py

Example mapping:

constitutional_ai/framework.py  →  tests/test_framework.py
constitutional_ai/trainer.py    →  tests/test_trainer.py
constitutional_ai/principles.py →  tests/test_principles.py

Test Function Naming

def test_{functionality}():
    """Test {what it does}."""
    pass

def test_{class}_{method}():
    """Test {Class}.{method} does {what}."""
    pass

def test_{edge_case}_raises_{exception}():
    """Test that {edge case} raises {ExceptionType}."""
    pass

Examples:

def test_framework_initialization():
    """Test ConstitutionalFramework initializes with default principles."""

def test_evaluate_text_returns_dict():
    """Test evaluate_text returns dictionary with expected keys."""

def test_invalid_principle_raises_value_error():
    """Test that invalid principle configuration raises ValueError."""

Pytest Core Patterns

Basic Test Structure

import pytest
from constitutional_ai import ConstitutionalFramework


def test_example():
    # Arrange
    framework = ConstitutionalFramework()

    # Act
    result = framework.evaluate_text("test input")

    # Assert
    assert result is not None
    assert 'any_flagged' in result

Fixtures for Setup

@pytest.fixture
def framework():
    """Provide a configured ConstitutionalFramework for tests."""
    from constitutional_ai import setup_default_framework
    return setup_default_framework()


@pytest.fixture
def mock_model():
    """Provide a mock model for testing."""
    from tests.mocks.mock_model import MockModel
    return MockModel()


def test_with_fixtures(framework, mock_model):
    """Test using fixtures."""
    result = framework.evaluate_text("test", model=mock_model)
    assert result['any_flagged'] == False

Parametrized Tests

@pytest.mark.parametrize("input_text,expected_flagged", [
    ("helpful response", False),
    ("harmful content", True),
    ("neutral statement", False),
])
def test_evaluation_cases(framework, input_text, expected_flagged):
    """Test evaluation with various inputs."""
    result = framework.evaluate_text(input_text)
    assert result['any_flagged'] == expected_flagged

Testing Exceptions

def test_invalid_input_raises():
    """Test that invalid input raises ValueError."""
    framework = ConstitutionalFramework()

    with pytest.raises(ValueError, match="must not be empty"):
        framework.evaluate_text("")


def test_missing_model_raises():
    """Test that missing model raises appropriate error."""
    with pytest.raises(RuntimeError):
        generate_text(prompt="test", model=None, tokenizer=None)

Mocking AI Components

Use Project Mocks

The project has mocks in tests/mocks/ directory:

from tests.mocks.mock_model import MockModel
from tests.mocks.mock_tokenizer import MockTokenizer

def test_with_mock_model():
    """Test using mock model for deterministic results."""
    model = MockModel()
    tokenizer = MockTokenizer()

    # Mock returns predictable outputs
    output = model.generate(inputs)
    assert output is not None

Why Mock AI Components?

1. Determinism: Real models are stochastic
2. Speed: Avoid expensive model loading/inference
3. Isolation: Test logic independently of model behavior
4. Portability: Tests run without GPU or large models

When to Mock vs Real Models

# ✅ Mock for unit tests
def test_critique_revision_logic():
    """Test critique-revision pipeline logic."""
    model = MockModel()  # Fast, deterministic
    # Test the pipeline logic, not model quality

# ✅ Real model for integration tests (marked slow)
@pytest.mark.slow
def test_end_to_end_training():
    """Test full training pipeline with real model."""
    model = load_model("gpt2")  # Real model
    # Test complete system integration

Coverage Best Practices

Project Coverage Target

• Current: ~45% coverage
• Target: This is acceptable for ML research code
• Why: Training loops, model internals are hard to test exhaustively

Focus Testing On

1. Framework logic (high value, testable)

   • Principle management
   • Evaluation logic
   • Configuration handling

2. Data processing (deterministic, testable)

   • Dataset creation
   • Tokenization
   • Preference pair generation

3. Edge cases (prevent regressions)

   • Empty inputs
   • Invalid configurations
   • Missing dependencies

Skip Detailed Testing For

1. Model internals (PyTorch's responsibility)
2. Stochastic generation (unless mocked)
3. Long training runs (expensive, flaky)

Test Organization Patterns

Grouping with Classes

class TestConstitutionalFramework:
    """Tests for ConstitutionalFramework class."""

    def test_initialization(self):
        """Test framework initializes correctly."""
        framework = ConstitutionalFramework()
        assert framework is not None

    def test_add_principle(self):
        """Test adding a principle."""
        framework = ConstitutionalFramework()
        principle = ConstitutionalPrinciple(name="test", weight=1.0)
        framework.add_principle(principle)
        assert "test" in framework.principles

Setup and Teardown

class TestWithSetup:
    def setup_method(self):
        """Run before each test method."""
        self.framework = setup_default_framework()

    def teardown_method(self):
        """Run after each test method."""
        # Cleanup if needed
        pass

    def test_example(self):
        """Test using setup."""
        result = self.framework.evaluate_text("test")
        assert result is not None

Running Tests (Common Commands)

All tests

pytest tests/ -v

With coverage

pytest tests/ --cov=constitutional_ai --cov-report=term-missing

Specific module

pytest tests/test_framework.py -v

Stop on first failure

pytest tests/ -x

Only failed tests from last run

pytest tests/ --lf

Parallel execution

pytest tests/ -n auto

Slow tests only

pytest tests/ -m slow

Skip slow tests

pytest tests/ -m "not slow"

Test Quality Checklist

Before committing tests:

• Test file named test_{module}.py
• Test functions named test_{functionality}
• Docstrings explain what is being tested
• AI components mocked for determinism
• Edge cases covered (empty inputs, invalid configs)
• Assertions are specific and meaningful
• Tests are independent (no shared state)
• Fast tests are unmarked, slow tests marked @pytest.mark.slow

Current Test Status

Metrics:

• Total tests: 658
• Passing: ~100% (after recent fixes)
• Coverage: ~45% (acceptable for ML code)
• Test files: 14

Key test modules:

• test_framework.py - Framework and principle management
• test_principles.py - Evaluation functions
• test_critique_revision.py - Phase 1 pipeline
• test_reward_model.py - Reward model training
• test_ppo_trainer.py - PPO optimization
• test_trainer.py - Supervised fine-tuning
• test_evaluator.py - Evaluation logic
• test_model_utils.py - Model loading and generation

Example: Complete Test File Template

"""Tests for constitutional_ai/{module}.py"""
import pytest
from constitutional_ai import SomeClass
from tests.mocks.mock_model import MockModel


@pytest.fixture
def instance():
    """Provide configured instance for testing."""
    return SomeClass()


class TestSomeClass:
    """Tests for SomeClass."""

    def test_initialization(self, instance):
        """Test SomeClass initializes correctly."""
        assert instance is not None

    def test_method(self, instance):
        """Test method does expected thing."""
        result = instance.method("input")
        assert result == "expected"

    @pytest.mark.parametrize("input,expected", [
        ("a", 1),
        ("b", 2),
    ])
    def test_parametrized(self, instance, input, expected):
        """Test method with various inputs."""
        assert instance.method(input) == expected

    def test_edge_case_raises(self, instance):
        """Test edge case raises appropriate error."""
        with pytest.raises(ValueError):
            instance.method(None)


@pytest.mark.slow
def test_integration():
    """Test end-to-end with real components."""
    # Use real models, expensive operations
    pass