[network, test-only] document tagsObserver in unit tests

network/test/middleware_test.go

@@ -28,6 +28,11 @@ import (
 
 const testChannel = "test-channel"
 
+// libp2p emits a call to `Protect` with a topic-specific tag upon establishing each peering connection in a GossipSUb mesh, see:
+// https://github.com/libp2p/go-libp2p-pubsub/blob/master/tag_tracer.go
+// One way to make sure such a mesh has formed, asynchronously, in unit tests, is to wait for libp2p.GossipSubD such calls,
+// and that's what we do with tagsObserver.
+//
 type tagsObserver struct {
 	tags chan string
 	log  zerolog.Logger