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Testing Guide

✅ Conversion Complete: unittest → pytest

The test suite has been successfully converted from unittest to pytest!

🎯 Why pytest?

Advantages over unittest:

  1. Simpler syntax - No need to inherit from TestCase or use self.assert*
  2. Better output - More readable failure messages showing actual vs expected values
  3. Fixtures - More powerful and flexible setup/teardown with @pytest.fixture
  4. Parametrization - Easy to run same test with different inputs
  5. Less boilerplate - Just write functions, not classes
  6. Better assertion introspection - Automatically shows values in failures

Example Comparison:

unittest (old):

class TestParticle(unittest.TestCase):
    def setUp(self):
        self.position = np.array([1.0, 2.0])
        
    def test_kinetic_energy(self):
        particle = Particle(position=self.position, ...)
        self.assertAlmostEqual(particle.kinetic_energy, expected, places=5)

pytest (new):

@pytest.fixture
def particle_params():
    return {'position': np.array([1.0, 2.0])}

def test_kinetic_energy(particle_params):
    particle = Particle(position=particle_params['position'], ...)
    assert particle.kinetic_energy == pytest.approx(expected, rel=1e-5)

📦 Installation

Install dependencies:

pip install -r requirements.txt

Or install pytest directly:

pip install pytest pytest-cov

🚀 Running Tests

Basic commands:

# Run all tests
pytest tests/

# Run with verbose output
pytest tests/ -v

# Run specific test file
pytest tests/test_particle.py

# Run specific test function
pytest tests/test_particle.py::test_kinetic_energy_moving_particle

Advanced commands:

# Run with coverage report
pytest tests/ --cov=md_simulation --cov-report=term

# Generate HTML coverage report
pytest tests/ --cov=md_simulation --cov-report=html

# Run with detailed output
pytest tests/ -vv

# Show print statements
pytest tests/ -s

# Run only failed tests from last run
pytest tests/ --lf

# Stop at first failure
pytest tests/ -x

📊 Test Results

All 32 tests pass successfully:

=============================== test session starts ===============================
collected 32 items

tests/test_particle.py ........                                              [ 25%]
tests/test_potential.py ...............                                      [ 71%]
tests/test_simulation.py .........                                           [100%]

=============================== 32 passed in 0.78s ================================

Coverage:

  • 55% code coverage - Tests cover core functionality
  • Main simulation code: 250 statements, 138 covered

📝 Test Structure

Fixtures Used:

test_particle.py:

  • particle_params - Common particle parameters (position, velocity, mass)

test_potential.py:

  • lj_potential - LennardJonesPotential instance with Argon parameters
  • lj_params - Dictionary of Lennard-Jones parameters

test_simulation.py:

  • lj_potential - Lennard-Jones potential for simulations
  • particles - Tuple of two particles (one moving, one fixed)
  • simulation - Complete TwoParticleMD simulation instance

Test Coverage:

Particle Tests (8 tests):

  • ✅ Initialization
  • ✅ Kinetic energy (moving, fixed, stationary)
  • ✅ Property mutability

Potential Tests (15 tests):

  • ✅ Initialization
  • ✅ Potential energy at various distances
  • ✅ Force magnitude and direction
  • ✅ Repulsive vs attractive regimes
  • ✅ 2D force vectors

Simulation Tests (9 tests):

  • ✅ Initialization
  • ✅ Energy calculation and conservation
  • ✅ Time stepping
  • ✅ Wall collisions
  • ✅ Fixed particle behavior
  • ✅ History recording

🔧 Adding New Tests

Create a new test file or add to existing ones:

import pytest
import numpy as np
from md_simulation import Particle

@pytest.fixture
def my_fixture():
    """Fixture providing test data."""
    return {'value': 42}

def test_something(my_fixture):
    """Test description."""
    result = calculate_something(my_fixture['value'])
    assert result == expected_value

def test_with_approx():
    """Test floating point comparison."""
    result = 3.14159265
    assert result == pytest.approx(3.14159, rel=1e-5)

def test_array_comparison():
    """Test numpy array comparison."""
    result = np.array([1.0, 2.0, 3.0])
    expected = np.array([1.0, 2.0, 3.0])
    np.testing.assert_array_equal(result, expected)

🎓 Pytest Features

Parametrization:

@pytest.mark.parametrize("input,expected", [
    (1, 2),
    (2, 4),
    (3, 6),
])
def test_double(input, expected):
    assert input * 2 == expected

Markers:

@pytest.mark.slow
def test_long_running():
    # Long test
    pass

# Run only slow tests: pytest -m slow
# Skip slow tests: pytest -m "not slow"

Exception testing:

def test_raises_error():
    with pytest.raises(ValueError):
        raise ValueError("Expected error")

📚 Resources

🎉 Summary

✅ All tests converted from unittest to pytest
✅ All 32 tests passing
✅ 55% code coverage
✅ Cleaner, more readable test code
✅ Better error messages
✅ Fixtures for reusable test setup
✅ Coverage reporting enabled