[release-18.0] TestStreamMigrateMainflow: fix panic in test (#14425)

Signed-off-by: Rohit Nayak <rohit@planetscale.com>

go/vt/wrangler/fake_tablet_test.go

@@ -23,6 +23,9 @@ import (
  "testing"
  "time"
 
+ vdiff2 "vitess.io/vitess/go/vt/vttablet/tabletmanager/vdiff"
+ "vitess.io/vitess/go/vt/vttablet/tabletserver/tabletenv"
+
  "github.com/stretchr/testify/require"
  "google.golang.org/grpc"
 
@@ -187,7 +190,7 @@ func (ft *fakeTablet) StartActionLoop(t *testing.T, wr *Wrangler) {
  ft.Tablet.PortMap["vt"] = vtPort
  ft.Tablet.PortMap["grpc"] = gRPCPort
  ft.Tablet.Hostname = "127.0.0.1"
-
+ config := &tabletenv.TabletConfig{}
  // Create a test tm on that port, and re-read the record
  // (it has new ports and IP).
  ft.TM = &tabletmanager.TabletManager{
@@ -196,6 +199,7 @@ func (ft *fakeTablet) StartActionLoop(t *testing.T, wr *Wrangler) {
  MysqlDaemon: ft.FakeMysqlDaemon,
  DBConfigs: &dbconfigs.DBConfigs{},
  QueryServiceControl: tabletservermock.NewController(),
+ VDiffEngine: vdiff2.NewEngine(config, wr.TopoServer(), ft.Tablet),
  }
  if err := ft.TM.Start(ft.Tablet, 0); err != nil {
  t.Fatal(err)