vrepl: yet another vstreamer deflake

The latest stream from "current" position feature introduced
a hang in the vstreamer, if the subsequent DMLs started getting
played before the vstreamer would start pulling from binlogs.

The fix is to wait till we get a heartbeat before proceeding
with the tests.

Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>

go/vt/vttablet/tabletserver/vstreamer/vstreamer_test.go

@@ -1083,11 +1083,17 @@ func TestHeartbeat(t *testing.T) {
  assert.Equal(t, binlogdatapb.VEventType_HEARTBEAT, evs[0].Type)
 }
 
-func runCases(t *testing.T, filter *binlogdatapb.Filter, testcases []testcase, postion string) {
+func runCases(t *testing.T, filter *binlogdatapb.Filter, testcases []testcase, position string) {
  t.Helper()
  ctx, cancel := context.WithCancel(context.Background())
  defer cancel()
- ch := startStream(ctx, t, filter, postion)
+ ch := startStream(ctx, t, filter, position)
+
+ // If position is 'current', we wait for a heartbeat to be
+ // sure the vstreamer has started.
+ if position == "current" {
+ <-ch
+ }
 
  for _, tcase := range testcases {
  switch input := tcase.input.(type) {
@@ -1108,6 +1114,8 @@ func runCases(t *testing.T, filter *binlogdatapb.Filter, testcases []testcase, p
 
 func expectLog(ctx context.Context, t *testing.T, input interface{}, ch <-chan []*binlogdatapb.VEvent, output [][]string) {
  t.Helper()
+ timer := time.NewTimer(1 * time.Minute)
+ defer timer.Stop()
  for _, wantset := range output {
  var evs []*binlogdatapb.VEvent
  for {
@@ -1125,6 +1133,8 @@ func expectLog(ctx context.Context, t *testing.T, input interface{}, ch <-chan [
  }
  case <-ctx.Done():
  t.Fatal("stream ended early")
+ case <-timer.C:
+ t.Fatalf("timed out waiting for events: %v", wantset)
  }
  if len(evs) != 0 {
  break