p2p/discover: fix flaky test which wrote to test.log after completion

p2p/discover/v4_lookup_test.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"net/netip"
 	"slices"
+	"sync"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/crypto"
@@ -75,7 +76,12 @@ func TestUDPv4_LookupIterator(t *testing.T) {
 		bootnodes[i] = lookupTestnet.node(256, i)
 	}
 	fillTable(test.table, bootnodes, true)
-	go serveTestnet(test, lookupTestnet)
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		serveTestnet(test, lookupTestnet)
+		wg.Done()
+	}()
 
 	// Create the iterator and collect the nodes it yields.
 	iter := test.udp.RandomNodes()
@@ -95,6 +101,8 @@ func TestUDPv4_LookupIterator(t *testing.T) {
 	if err := checkNodesEqual(results, want); err != nil {
 		t.Fatal(err)
 	}
+	test.close()
+	wg.Wait()
 }
 
 // TestUDPv4_LookupIteratorClose checks that lookupIterator ends when its Close
@@ -110,7 +118,13 @@ func TestUDPv4_LookupIteratorClose(t *testing.T) {
 		bootnodes[i] = lookupTestnet.node(256, i)
 	}
 	fillTable(test.table, bootnodes, true)
-	go serveTestnet(test, lookupTestnet)
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		serveTestnet(test, lookupTestnet)
+		wg.Done()
+	}()
 
 	it := test.udp.RandomNodes()
 	if ok := it.Next(); !ok || it.Node() == nil {
@@ -132,6 +146,8 @@ func TestUDPv4_LookupIteratorClose(t *testing.T) {
 	if n := it.Node(); n != nil {
 		t.Errorf("iterator returned non-nil node after close and %d more calls", ncalls)
 	}
+	test.close()
+	wg.Wait()
 }
 
 func serveTestnet(test *udpTest, testnet *preminedTestnet) {

p2p/enode/nodedb.go

@@ -496,6 +496,10 @@ func nextNode(it iterator.Iterator) *Node {
 
 // Close flushes and closes the database files.
 func (db *DB) Close() {
-	close(db.quit)
+	select {
+	case <-db.quit: // already closed
+	default:
+		close(db.quit)
+	}
 	db.lvl.Close()
 }