CG: More specific duplicated group error.

src/t_stream.c

@@ -1391,7 +1391,8 @@ NULL
         if (cg) {
             addReply(c,shared.ok);
         } else {
-            addReplyError(c,"Consumer Group name already exists");
+            addReplySds(c,
+                sdsnew("-BUSYGROUP Consumer Group name already exists\r\n"));
         }
     } else if (!strcasecmp(opt,"SETID") && c->argc == 5) {
     } else if (!strcasecmp(opt,"DELGROUP") && c->argc == 4) {

tests/unit/type/stream-cgroups.tcl

+start_server {
+    tags {"stream"}
+} {
+    test {XGROUP CREATE: creation and duplicate group name detection} {
+        r DEL mystream
+        r XADD mystream * foo bar
+        r XGROUP CREATE mystream mygroup $
+        catch {r XGROUP CREATE mystream mygroup $} err
+        set err
+    } {BUSYGROUP*}
+}