Implement comprehensive test suite for TagGen AI

[itsmattius]

The TagGen AI application currently lacks a comprehensive test suite, which is essential for maintaining code quality, preventing regressions, and ensuring reliable functionality.

Current State

• Limited test coverage
• No integration tests
• Missing unit tests for core functionality
• No automated testing pipeline

Required Test Coverage

• Unit tests for all services
• Integration tests for API endpoints
• AI provider testing (OpenAI, Transformers)
• Validation system testing
• Error handling tests
• Performance tests

Test Categories Needed

• Unit Tests: Individual component testing
• Integration Tests: API endpoint testing
• Mock Tests: AI provider mocking
• Validation Tests: Input/output validation
• Error Tests: Exception handling
• Performance Tests: Load and stress testing

Technical Details

• File: src/tests/__init__.py:0
• Current test structure is minimal
• Need to implement pytest framework
• Mock external dependencies

Acceptance Criteria

• Set up pytest testing framework
• Implement unit tests for all services
• Add integration tests for API endpoints
• Create mock tests for AI providers
• Add validation system tests
• Implement error handling tests
• Set up CI/CD testing pipeline
• Achieve >80% code coverage
• Add performance benchmarks