Implement unit tests and testing framework

Task Description

Implement comprehensive unit tests to ensure code reliability and maintainability.

Requirements

• Set up pytest testing framework
• Create test files for all main modules:
  • tests/test_data_preprocessing.py
  • tests/test_model.py
  • tests/test_utils.py
• Implement test cases covering:
  • Data loading and validation
  • Text preprocessing functions
  • Model training and prediction
  • Error handling scenarios
  • Edge cases

Test Coverage Areas

Data Preprocessing Tests

• Test text cleaning functions with various inputs
• Test preprocessing pipeline with edge cases
• Test data loading with valid/invalid files
• Test data statistics calculation

Model Tests

• Test model initialization
• Test training with different datasets
• Test prediction functionality
• Test model save/load operations
• Test evaluation metrics calculation

Integration Tests

• Test end-to-end pipeline
• Test model comparison functionality
• Test with different data formats

Testing Framework Setup

• Add pytest to requirements.txt
• Create pytest configuration file (pytest.ini or pyproject.toml)
• Set up test data fixtures
• Configure test coverage reporting

Acceptance Criteria

• All test files are created and properly structured
• Test coverage is at least 80%
• All tests pass successfully
• Tests include both positive and negative test cases
• Mock objects are used appropriately for external dependencies
• Test data fixtures are properly set up
• CI/CD integration is considered (GitHub Actions workflow)
• Tests are well-documented with clear descriptions