Create comprehensive test suite

Develop a test suite for TroubleKuber:

Features to implement

• Unit tests for core functions
• Integration tests with mock Kubernetes responses
• Test fixtures for various failure scenarios
• Automated testing in CI/CD pipeline
• Test coverage reporting

Implementation details

• Create tests/ directory with unit and integration subdirectories
• Add test framework (bats or similar)
• Create mock kubectl responses for testing
• Set up test fixtures for common failure scenarios
• Add test documentation