test: use meck in olp tests

avoid flaky test results by using mecks.

apps/emqx/test/emqx_olp_SUITE.erl

@@ -19,8 +19,6 @@
 -compile(export_all).
 -compile(nowarn_export_all).
 
--include_lib("emqx/include/emqx.hrl").
--include_lib("emqx/include/emqx_mqtt.hrl").
 -include_lib("eunit/include/eunit.hrl").
 -include_lib("common_test/include/ct.hrl").
 -include_lib("lc/include/lc.hrl").
@@ -61,61 +59,41 @@ t_disable_enable(_Config) ->
     ok = emqx_olp:disable(),
     ?assert(not is_process_alive(Old)),
     {ok, Pid} = emqx_olp:enable(),
-    timer:sleep(1000),
     ?assert(is_process_alive(Pid)).
 
 %% Test that overload detection works
 t_is_overloaded(_Config) ->
-    P = burst_runq(),
-    timer:sleep(3000),
+    meck:new(load_ctl, [passthrough]),
+    meck:expect(load_ctl, is_overloaded, fun() -> true end),
     ?assert(emqx_olp:is_overloaded()),
-    exit(P, kill),
-    timer:sleep(3000),
-    ?assert(not emqx_olp:is_overloaded()).
+    meck:expect(load_ctl, is_overloaded, fun() -> false end),
+    ?assert(not emqx_olp:is_overloaded()),
+    meck:unload(load_ctl).
 
 %% Test that new conn is rejected when olp is enabled
 t_overloaded_conn(_Config) ->
     process_flag(trap_exit, true),
     ?assert(erlang:is_process_alive(load_ctl:whereis_runq_flagman())),
     emqx_config:put([overload_protection, enable], true),
-    P = burst_runq(),
-    timer:sleep(1000),
+    meck:new(load_ctl, [passthrough]),
+    meck:expect(load_ctl, is_overloaded, fun() -> true end),
     ?assert(emqx_olp:is_overloaded()),
     true = emqx:is_running(node()),
     {ok, C} = emqtt:start_link([{host, "localhost"}, {clientid, "myclient"}]),
     ?assertNotMatch({ok, _Pid}, emqtt:connect(C)),
-    exit(P, kill).
+    meck:unload(load_ctl).
 
 %% Test that new conn is rejected when olp is enabled
 t_overload_cooldown_conn(Config) ->
     t_overloaded_conn(Config),
-    timer:sleep(1000),
+    meck:new(load_ctl, [passthrough]),
+    meck:expect(load_ctl, is_overloaded, fun() -> false end),
     ?assert(not emqx_olp:is_overloaded()),
     true = emqx:is_running(node()),
     {ok, C} = emqtt:start_link([{host, "localhost"}, {clientid, "myclient"}]),
     ?assertMatch({ok, _Pid}, emqtt:connect(C)),
-    emqtt:stop(C).
-
--spec burst_runq() -> ParentToKill :: pid().
-burst_runq() ->
-    NProc = erlang:system_info(schedulers_online),
-    spawn(?MODULE, worker_parent, [NProc * 1000, {?MODULE, busy_loop, []}]).
-
-%% internal helpers
-worker_parent(N, {M, F, A}) ->
-    lists:foreach(
-        fun(_) ->
-            proc_lib:spawn_link(fun() -> apply(M, F, A) end)
-        end,
-        lists:seq(1, N)
-    ),
-    receive
-        stop -> ok
-    end.
-
-busy_loop() ->
-    erlang:yield(),
-    busy_loop().
+    emqtt:stop(C),
+    meck:unload(load_ctl).
 
 wait_for(_Fun, 0) ->
     false;