diff --git a/test/emqx_vm_mon_SUITE.erl b/test/emqx_vm_mon_SUITE.erl
index cb85b1fac..2b26c8078 100644
--- a/test/emqx_vm_mon_SUITE.erl
+++ b/test/emqx_vm_mon_SUITE.erl
@@ -39,18 +39,6 @@ init_per_suite(Config) ->
 end_per_suite(_Config) ->
     application:stop(sasl).
     
-    t_get_process_high_watermark(_) ->
-    error('TODO').
-
-t_set_process_high_watermark(_) ->
-    error('TODO').
-
-t_get_process_low_watermark(_) ->
-    error('TODO').
-
-t_set_process_low_watermark(_) ->
-    error('TODO').
-
 t_api(_) ->
     meck:new(alarm_handler, [passthrough, no_history]),
     Tester = self(),
@@ -70,8 +58,13 @@ t_api(_) ->
                     end),
         gen_event:swap_handler(alarm_handler, {emqx_alarm_handler, swap}, {alarm_handler, []}),
         {ok, _} = emqx_vm_mon:start_link([{check_interval, 1},
-                                        {process_high_watermark, 0},
-                                        {process_low_watermark, 0.6}]),
+                                        {process_high_watermark, 0.8},
+                                        {process_low_watermark, 0.75}]),
+        timer:sleep(emqx_vm_mon:get_check_interval() * 1000),
+        emqx_vm_mon:set_process_high_watermark(0.0),
+        emqx_vm_mon:set_process_low_watermark(0.6),
+        ?assertEqual(0.0, emqx_vm_mon:get_process_high_watermark()),
+        ?assertEqual(0.6, emqx_vm_mon:get_process_low_watermark()),
         ?WAIT({Ref, set_alarm, {too_many_processes, _Count}}, 2000),
         ?assertEqual(true, lists:keymember(too_many_processes, 1, alarm_handler:get_alarms())),
         emqx_vm_mon:set_process_high_watermark(0.8),
@@ -81,7 +74,10 @@ t_api(_) ->
         ?WAIT({Ref, clear_alarm, too_many_processes}, 3000),
         ?assertEqual(false, lists:keymember(too_many_processes, 1, alarm_handler:get_alarms())),
         emqx_vm_mon:set_check_interval(20),
-        ?assertEqual(20, emqx_vm_mon:get_check_interval())
+        ?assertEqual(20, emqx_vm_mon:get_check_interval()),
+        ?assertEqual(ignored, gen_server:call(emqx_vm_mon, ignored)),
+        ?assertEqual(ok, gen_server:cast(emqx_vm_mon, ignored)),
+        ?assertEqual(ignored, emqx_vm_mon ! ignored)
     after
         meck:unload(alarm_handler)
     end.