test(trie): add more involved route add + delete case

That shows how current local trie implementation breaks because
of lack of refcounting.

apps/emqx/test/emqx_router_SUITE.erl

@@ -79,6 +79,55 @@ t_add_delete(_) ->
     ?R:delete_route(<<"a/+/b">>, node()),
     ?assertEqual([], ?R:topics()).
 
+t_add_delete_incremental(_) ->
+    ?R:add_route(<<"a/b/c">>),
+    ?R:add_route(<<"a/+/c">>, node()),
+    ?R:add_route(<<"a/+/+">>, node()),
+    ?R:add_route(<<"a/b/#">>, node()),
+    ?R:add_route(<<"#">>, node()),
+    ?assertEqual(
+        [
+            #route{topic = <<"#">>, dest = node()},
+            #route{topic = <<"a/+/+">>, dest = node()},
+            #route{topic = <<"a/+/c">>, dest = node()},
+            #route{topic = <<"a/b/#">>, dest = node()},
+            #route{topic = <<"a/b/c">>, dest = node()}
+        ],
+        lists:sort(?R:match_routes(<<"a/b/c">>))
+    ),
+    ?R:delete_route(<<"a/+/c">>, node()),
+    ?assertEqual(
+        [
+            #route{topic = <<"#">>, dest = node()},
+            #route{topic = <<"a/+/+">>, dest = node()},
+            #route{topic = <<"a/b/#">>, dest = node()},
+            #route{topic = <<"a/b/c">>, dest = node()}
+        ],
+        lists:sort(?R:match_routes(<<"a/b/c">>))
+    ),
+    ?R:delete_route(<<"a/+/+">>, node()),
+    ?assertEqual(
+        [
+            #route{topic = <<"#">>, dest = node()},
+            #route{topic = <<"a/b/#">>, dest = node()},
+            #route{topic = <<"a/b/c">>, dest = node()}
+        ],
+        lists:sort(?R:match_routes(<<"a/b/c">>))
+    ),
+    ?R:delete_route(<<"a/b/#">>, node()),
+    ?assertEqual(
+        [
+            #route{topic = <<"#">>, dest = node()},
+            #route{topic = <<"a/b/c">>, dest = node()}
+        ],
+        lists:sort(?R:match_routes(<<"a/b/c">>))
+    ),
+    ?R:delete_route(<<"a/b/c">>, node()),
+    ?assertEqual(
+        [#route{topic = <<"#">>, dest = node()}],
+        lists:sort(?R:match_routes(<<"a/b/c">>))
+    ).
+
 t_do_add_delete(_) ->
     ?R:do_add_route(<<"a/b/c">>),
     ?R:do_add_route(<<"a/b/c">>, node()),