integration: fix "TestV3WatchMultipleStreams"

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

integration/v3_watch_test.go

@@ -921,6 +921,9 @@ func testV3WatchMultipleStreams(t *testing.T, startRev int64) {
 			Kv:   &mvccpb.KeyValue{Key: []byte("foo"), Value: []byte("bar"), CreateRevision: 2, ModRevision: 2, Version: 1},
 		},
 	}
+
+	var idMu sync.Mutex
+	ids := make(map[int64]struct{})
 	for i := range streams {
 		go func(i int) {
 			defer wg.Done()
@@ -929,9 +932,12 @@ func testV3WatchMultipleStreams(t *testing.T, startRev int64) {
 			if err != nil {
 				t.Fatalf("wStream.Recv error: %v", err)
 			}
-			if wresp.WatchId != 0 {
-				t.Errorf("watchId got = %d, want = 0", wresp.WatchId)
+			idMu.Lock()
+			if _, ok := ids[wresp.WatchId]; ok {
+				t.Fatalf("duplicate watch ID found %d", wresp.WatchId)
 			}
+			ids[wresp.WatchId] = struct{}{}
+			idMu.Unlock()
 			if !reflect.DeepEqual(wresp.Events, wevents) {
 				t.Errorf("wresp.Events got = %+v, want = %+v", wresp.Events, wevents)
 			}