docs: Document testing and code style requirements

[AngusHsu]

Description

Document testing requirements and code style guidelines.

Parent Epic

#10 - Add CONTRIBUTING.md guide

Testing Requirements

Coverage Targets

• Document minimum 80% line coverage
• Document minimum 70% branch coverage
• Explain coverage measurement

Test Structure

• Unit test organization
• Test naming conventions
• Test file locations
• Running specific tests

Test Categories

• Valid ID tests (positive cases)
• Invalid ID tests (negative cases)
• Edge case tests
• Parse function tests

Code Style

TypeScript Guidelines

• Strict mode requirements
• Type annotation standards
• Naming conventions

Linting

• ESLint configuration
• Prettier configuration
• Pre-commit hooks

Code Organization

• File structure
• Export patterns
• Comment standards

Acceptance Criteria

• Testing requirements documented
• Code style guide complete
• Examples provided

Labels

documentation, testing, code-style