fix: flaky test on twopc transaction (#17068)

Signed-off-by: Harshit Gangal <[email protected]>

go/test/endtoend/transaction/twopc/main_test.go

@@ -168,24 +168,21 @@ func getDTID(dtidMap map[string]string, dtKey string) string {
 }
 
 func runVStream(t *testing.T, ctx context.Context, ch chan *binlogdatapb.VEvent, vtgateConn *vtgateconn.VTGateConn) {
-	vgtid := &binlogdatapb.VGtid{
-		ShardGtids: []*binlogdatapb.ShardGtid{
-			{Keyspace: keyspaceName, Shard: "-40", Gtid: "current"},
-			{Keyspace: keyspaceName, Shard: "40-80", Gtid: "current"},
-			{Keyspace: keyspaceName, Shard: "80-", Gtid: "current"},
-		}}
-	filter := &binlogdatapb.Filter{
-		Rules: []*binlogdatapb.Rule{{
-			Match: "/.*/",
-		}},
+	shards := []string{"-40", "40-80", "80-"}
+	shardGtids := make([]*binlogdatapb.ShardGtid, 0, len(shards))
+	var seen = make(map[string]bool, len(shards))
+	var wg sync.WaitGroup
+	for _, shard := range shards {
+		shardGtids = append(shardGtids, &binlogdatapb.ShardGtid{Keyspace: keyspaceName, Shard: shard, Gtid: "current"})
+		seen[shard] = false
+		wg.Add(1)
 	}
+	vgtid := &binlogdatapb.VGtid{ShardGtids: shardGtids}
+	filter := &binlogdatapb.Filter{Rules: []*binlogdatapb.Rule{{Match: "/.*/"}}}
+
 	vReader, err := vtgateConn.VStream(ctx, topodatapb.TabletType_PRIMARY, vgtid, filter, nil)
 	require.NoError(t, err)
 
-	// Use a channel to signal that the first VGTID event has been processed
-	firstEventProcessed := make(chan struct{})
-	var once sync.Once
-
 	go func() {
 		for {
 			evs, err := vReader.Recv()
@@ -195,9 +192,12 @@ func runVStream(t *testing.T, ctx context.Context, ch chan *binlogdatapb.VEvent,
 			require.NoError(t, err)
 
 			for _, ev := range evs {
-				// Signal the first event has been processed using sync.Once
+				// Mark VGTID event from each shard seen.
 				if ev.Type == binlogdatapb.VEventType_VGTID {
-					once.Do(func() { close(firstEventProcessed) })
+					if !seen[ev.Shard] {
+						seen[ev.Shard] = true
+						wg.Done()
+					}
 				}
 				if ev.Type == binlogdatapb.VEventType_ROW || ev.Type == binlogdatapb.VEventType_FIELD {
 					ch <- ev
@@ -206,8 +206,8 @@ func runVStream(t *testing.T, ctx context.Context, ch chan *binlogdatapb.VEvent,
 		}
 	}()
 
-	// Wait for the first event to be processed
-	<-firstEventProcessed
+	// Wait for VGTID event from all shards
+	wg.Wait()
 }
 
 func retrieveTransitions(t *testing.T, ch chan *binlogdatapb.VEvent, tableMap map[string][]*querypb.Field, dtMap map[string]string) map[string][]string {