Improve documentation and tests.

CHANGELOG.md

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+# Changelog
+
+All notable changes to the NetTest project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+- Comprehensive documentation with extensive doctests
+- Integration test examples demonstrating all major features
+- Enhanced README with detailed usage examples
+- Library-level documentation in src/lib.rs
+- Cargo.toml metadata for docs.rs integration
+
+### Changed
+- Improved API documentation with real-world examples
+- Enhanced error messages and debugging information
+
+## [0.1.0] - 2024-01-15
+
+### Added
+- **DNS Testing**
+  - Comprehensive DNS resolution testing with multiple record types
+  - Support for 23 traditional DNS servers including Google, Cloudflare, Quad9, OpenDNS, AdGuard
+  - System DNS resolver integration with EDNS0 support
+  - DNS sinkhole detection and security analysis
+  - Smart error handling distinguishing between failures and missing records
+  - Support for A, AAAA, MX, NS, TXT, CNAME, SOA, PTR, and DNSSEC record types
+
+- **DNS-over-HTTPS (DoH) Support**
+  - 16 DoH providers with comprehensive coverage
+  - Support for both JSON and Wire format protocols (RFC 8484)
+  - Provider variants for security filtering (malware blocking, family filters)
+  - Automatic format detection and provider-specific optimizations
+  - Google, Cloudflare, Quad9, OpenDNS, and AdGuard DoH endpoints
+
+- **Network Connectivity Testing**
+  - TCP and UDP connection testing with IPv4/IPv6 support
+  - ICMP ping tests with optional sudo privileges
+  - Common port scanning functionality
+  - Configurable timeouts and retry logic
+  - Cross-platform compatibility (macOS, Linux, Windows)
+
+- **MTU Discovery**
+  - Binary search MTU path discovery algorithm  
+  - Common MTU size testing (68, 576, 1280, 1492, 1500, 4464, 9000)
+  - Custom MTU range testing capabilities
+  - IPv6-aware MTU validation (1280 byte minimum)
+  - Optional sudo support for accurate ICMP-based discovery
+
+- **Security Analysis**
+  - DNS filtering effectiveness analysis
+  - Domain category testing (normal, ads, spam, adult, malicious, social, streaming, gaming, news)
+  - Sinkhole IP detection (0.0.0.0, 127.x.x.x, common filtering IPs)
+  - Security-focused DNS provider testing
+
+- **CLI Interface**
+  - Comprehensive command-line interface with subcommands
+  - Human-readable output with colored formatting
+  - JSON output format for integration with other tools
+  - Progress indicators for long-running operations
+  - Verbose logging support
+
+- **Performance Features**
+  - Async/concurrent testing architecture
+  - Parallel DNS provider testing (up to 39 simultaneous queries)
+  - Efficient binary search algorithms for MTU discovery
+  - Connection pooling and timeout optimization
+  - EDNS0 support for large DNS responses
+
+### Technical Details
+- **Dependencies**: Built with Tokio for async networking, Hickory DNS for resolution, Reqwest for HTTP
+- **Architecture**: Modular design with separate modules for DNS, network, MTU, and utilities
+- **Error Handling**: Comprehensive error types with detailed error messages
+- **Testing**: Extensive test suite with unit tests, integration tests, and doctests
+- **Documentation**: Complete API documentation with examples and usage patterns
+
+### Performance Benchmarks
+- DNS queries: 5-50ms for traditional DNS, 50-200ms for DoH
+- MTU discovery: Binary search completes in < 10 iterations for typical ranges
+- Concurrent testing: 39 DNS providers tested simultaneously
+- Memory usage: Efficient async implementation with minimal resource usage
+
+### Compatibility
+- **Rust Version**: 1.70+ required
+- **Platforms**: macOS, Linux, Windows
+- **IPv6**: Full IPv6 support alongside IPv4
+- **Privileges**: Optional sudo support for enhanced ICMP and MTU testing
+
+### Known Limitations
+- ICMP ping may require elevated privileges on some systems
+- MTU discovery accuracy depends on network path characteristics
+- Some DoH providers may have rate limiting
+- IPv6 connectivity depends on network infrastructure support