README.md

Unittest to Pytest Migration Example

This codemod demonstrates how to automatically migrate unittest test suites to pytest using Codegen. The migration script simplifies the process by handling all the tedious manual updates automatically.

How the Migration Script Works

The script automates the entire migration process in a few key steps:

1. Convert Test Classes and Setup Methods

   # From:
   class TestUsers(unittest.TestCase):
       def setUp(self):
           self.db = setup_test_db()
           
       def test_create_user(self):
           user = self.db.create_user("test")
           self.assertEqual(user.name, "test")
   
   # To:
   @pytest.fixture
   def db():
       db = setup_test_db()
       yield db
   
   def test_create_user(db):
       user = db.create_user("test")
       assert user.name == "test"

   • Converts unittest.TestCase classes to standalone functions
   • Replaces setUp methods with pytest fixtures

2. Update Assertions

   # From:
   def test_validation(self):
       self.assertTrue(is_valid("test"))
       self.assertEqual(count_items(), 0)
       self.assertRaises(ValueError, parse_id, "invalid")
   
   # To:
   def test_validation():
       assert is_valid("test")
       assert count_items() == 0
       with pytest.raises(ValueError):
           parse_id("invalid")

   • Replaces unittest assertions with pytest assertions
   • Uses pytest.raises for exception testing

3. Convert Test Discovery

   # From:
   if __name__ == '__main__':
       unittest.main()
   
   # To:
   # Remove unittest.main() and rename files to test_*.py

   • Removes unittest.main() calls
   • Ensures files are named for pytest discovery

4. Modernize Fixtures

   # From:
   @classmethod
   def setUpClass(cls):
       cls.conn = create_db()
   
   # To:
   @pytest.fixture(scope="session")
   def conn():
       return create_db()

   • Converts class-level setup to session-scoped fixtures

Running the Migration

# Install Codegen
pip install codegen

# Run the migration
python run.py

The script will process all Python test files in the repo-before directory and apply the transformations in the correct order.

Understanding the Code

• run.py - The migration script
• repo-before/ - Sample unittest test suite to migrate
• guide.md - Additional notes and explanations

Learn More

• Full Tutorial
• pytest Documentation
• unittest Documentation
• Codegen Documentation

Contributing

Feel free to submit issues and enhancement requests!