Future-proof Testing (Expansive protocol test coverage) 🧪

eta: 2023Q3

**Why:** Having interoperability tests with lots of transports, encryption mechanisms, and stream muxers is great. However, we need to stay backwards-compatible with legacy libp2p releases, with other libp2p implementations, and less advanced libp2p stacks.

**Goal:** Expand beyond unit tests and have expansive test-plan coverage that covers all protocols.

```[tasklist]
### Tasks
- [ ] https://github.com/libp2p/test-plans/issues/126
- [ ] https://github.com/libp2p/test-plans/issues/52
- [ ] https://github.com/libp2p/test-plans/issues/116
- [ ] https://github.com/libp2p/test-plans/issues/124
- [ ] GossipSub tests
- [ ] Kad DHT tests
- [ ] https://github.com/libp2p/test-plans/issues/195
```

Start by reviewing the linked test-plans issues 126, 52, 116, 124, and 195, along with the GossipSub and Kad DHT tasks. Use their scopes to define interoperability coverage for transports, encryption mechanisms, stream muxers, legacy libp2p releases, other implementations, and less advanced stacks. Done means expanding protocol coverage beyond unit tests.

Written by the indexing model from the issue text.