test: add E2E test for node peering (#5465)

This was a missing test case from the old P2P tests removed in #5453, which makes sure that all nodes are able to peer with each other regardless of how they discover peers.

Fixes #2795, since the default CI testnet uses a combination of (partially meshed) persistent peers and PEX-based seed nodes.

test/e2e/tests/net_test.go

@@ -0,0 +1,42 @@
+package e2e_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	e2e "github.com/tendermint/tendermint/test/e2e/pkg"
+)
+
+// Tests that all nodes have peered with each other, regardless of discovery method.
+func TestNet_Peers(t *testing.T) {
+	testNode(t, func(t *testing.T, node e2e.Node) {
+		// Seed nodes shouldn't necessarily mesh with the entire network.
+		if node.Mode == e2e.ModeSeed {
+			return
+		}
+
+		client, err := node.Client()
+		require.NoError(t, err)
+		netInfo, err := client.NetInfo(ctx)
+		require.NoError(t, err)
+
+		require.Equal(t, len(node.Testnet.Nodes)-1, netInfo.NPeers,
+			"node is not fully meshed with peers")
+
+		seen := map[string]bool{}
+		for _, n := range node.Testnet.Nodes {
+			seen[n.Name] = (n.Name == node.Name) // we've clearly seen ourself
+		}
+		for _, peerInfo := range netInfo.Peers {
+			peer := node.Testnet.LookupNode(peerInfo.NodeInfo.Moniker)
+			require.NotNil(t, peer, "unknown node %v", peerInfo.NodeInfo.Moniker)
+			require.Equal(t, peer.IP.String(), peerInfo.RemoteIP,
+				"unexpected IP address for peer %v", peer.Name)
+			seen[peerInfo.NodeInfo.Moniker] = true
+		}
+
+		for name := range seen {
+			require.True(t, seen[name], "node %v not peered with %v", node.Name, name)
+		}
+	})
+}