Add random kill in registry's concurrency test.

test/syn_pg_SUITE.erl

@@ -1673,10 +1673,12 @@ four_nodes_concurrency(Config) ->
             %% loop
             RandomMeta = rand:uniform(99999),
             ok = syn:join(scope_all, <<"concurrent-scope">>, Pid, RandomMeta),
+            %% random leave
             case rand:uniform(5) of
                 1 -> syn:leave(scope_all, <<"concurrent-scope">>, Pid);
                 _ -> ok
             end,
+            %% random sleep
             RndTime = rand:uniform(30),
             timer:sleep(RndTime)
         end, lists:seq(1, Iterations)),

test/syn_registry_SUITE.erl

@@ -1488,6 +1488,12 @@ four_nodes_concurrency(Config) ->
                             syn:register(scope_all, <<"concurrent">>, Pid, RandomMeta)
                     end
             end,
+            %% random kill
+            case rand:uniform(10) of
+                1 -> exit(Pid, kill);
+                _ -> ok
+            end,
+            %% random sleep
             RndTime = rand:uniform(30),
             timer:sleep(RndTime)
         end, lists:seq(1, Iterations)),