Add additional libp2p tests (#1867)

## Issue Addressed

N/A

## Proposed Changes

Adds tests for the eth2_libp2p crate.

beacon_node/network/src/attestation_service/mod.rs

@@ -38,7 +38,7 @@ const ADVANCE_SUBSCRIBE_TIME: u32 = 3;
 ///  36s at 12s slot time
 const DEFAULT_EXPIRATION_TIMEOUT: u32 = 3;
 
-#[derive(Debug, PartialEq, Clone)]
+#[derive(Debug, Clone)]
 pub enum AttServiceMessage {
     /// Subscribe to the specified subnet id.
     Subscribe(SubnetId),
@@ -52,6 +52,32 @@ pub enum AttServiceMessage {
     DiscoverPeers(Vec<SubnetDiscovery>),
 }
 
+/// Note: This `PartialEq` impl is for use only in tests.
+/// The `DiscoverPeers` comparison is good enough for testing only.
+#[cfg(test)]
+impl PartialEq for AttServiceMessage {
+    fn eq(&self, other: &AttServiceMessage) -> bool {
+        match (self, other) {
+            (AttServiceMessage::Subscribe(a), AttServiceMessage::Subscribe(b)) => a == b,
+            (AttServiceMessage::Unsubscribe(a), AttServiceMessage::Unsubscribe(b)) => a == b,
+            (AttServiceMessage::EnrAdd(a), AttServiceMessage::EnrAdd(b)) => a == b,
+            (AttServiceMessage::EnrRemove(a), AttServiceMessage::EnrRemove(b)) => a == b,
+            (AttServiceMessage::DiscoverPeers(a), AttServiceMessage::DiscoverPeers(b)) => {
+                if a.len() != b.len() {
+                    return false;
+                }
+                for i in 0..a.len() {
+                    if a[i].subnet_id != b[i].subnet_id || a[i].min_ttl != b[i].min_ttl {
+                        return false;
+                    }
+                }
+                true
+            }
+            _ => false,
+        }
+    }
+}
+
 /// A particular subnet at a given slot.
 #[derive(PartialEq, Eq, Hash, Clone, Debug)]
 pub struct ExactSubnet {