I'd like to mention that although I haven't been able to work on GitHub - swift-dns/swift-dns: A high-performance Swift DNS library built on top of SwiftNIO; aiming to provide DNS client, resolver and server implementations. · GitHub much lately, it does already have a good implementation of all DNS types in the DNSModels.
My memory is getting a bit rusty regarding it, but I know the impls are somewhat complete (e.g. contains DNSSEC as well), and that I have added a bunch of tests that run over packets I've captured via Wireshark. There are also integration tests that run against a real DNS server (was it Google's or Cloudflare's?, can't recall).
There are some benchmarks as well.
I also had plans for more test coverage and perhaps using existing test suites or such (example, Bonjour Conformance Test for mDNS), but did not get to that yet (mDNS specifically is not implemented anyway).
This is also related to: Requirements for IP address and port APIs - #3 by MahdiBM
swift-dns is where I noticed we lack such basic types and started putting those types together. swift-endpoint stuff used to be part of swift-dns before I decouple them. See [Pitch] Standard Network Address types if you're curious about the history.