feat: improve logging for speedtest connections

part of #7963

improve connection logging for speedtest connections

agent/agent.go

@@ -895,6 +895,10 @@ func (a *agent) createTailnet(ctx context.Context, agentID uuid.UUID, derpMap *t
 				}
 				break
 			}
+			clog := a.logger.Named("speedtest").With(
+				slog.F("remote", conn.RemoteAddr().String()),
+				slog.F("local", conn.LocalAddr().String()))
+			clog.Info(ctx, "accepted conn")
 			wg.Add(1)
 			closed := make(chan struct{})
 			go func() {
@@ -907,7 +911,12 @@ func (a *agent) createTailnet(ctx context.Context, agentID uuid.UUID, derpMap *t
 			}()
 			go func() {
 				defer close(closed)
-				_ = speedtest.ServeConn(conn)
+				sErr := speedtest.ServeConn(conn)
+				if sErr != nil {
+					clog.Error(ctx, "test ended with error", slog.Error(sErr))
+					return
+				}
+				clog.Info(ctx, "test ended")
 			}()
 		}
 		wg.Wait()

agent/agent_test.go

@@ -1850,13 +1850,16 @@ func TestAgent_UpdatedDERP(t *testing.T) {
 func TestAgent_Speedtest(t *testing.T) {
 	t.Parallel()
 	t.Skip("This test is relatively flakey because of Tailscale's speedtest code...")
+	logger := slogtest.Make(t, &slogtest.Options{IgnoreErrors: true}).Leveled(slog.LevelDebug)
 	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
 	defer cancel()
 	derpMap, _ := tailnettest.RunDERPAndSTUN(t)
 	//nolint:dogsled
 	conn, _, _, _, _ := setupAgent(t, agentsdk.Manifest{
 		DERPMap: derpMap,
-	}, 0)
+	}, 0, func(client *agenttest.Client, options *agent.Options) {
+		options.Logger = logger.Named("agent")
+	})
 	defer conn.Close()
 	res, err := conn.Speedtest(ctx, speedtest.Upload, 250*time.Millisecond)
 	require.NoError(t, err)