test: add test coverage for emqx_observer_cli

apps/emqx_modules/src/emqx_observer_cli.erl

@@ -35,17 +35,23 @@ disable() ->
 cmd(["status"]) ->
     observer_cli:start();
 cmd(["bin_leak"]) ->
-    [emqx_ctl:print("~p~n", [Row]) || Row <- recon:bin_leak(100)];
+    lists:foreach(
+        fun(Row) -> emqx_ctl:print("~p~n", [Row]) end,
+        recon:bin_leak(100)
+    );
 cmd(["load", Mod]) ->
     Module = list_to_existing_atom(Mod),
     Nodes = nodes(),
     Res = remote_load(Nodes, Module),
-    emqx_ctl:print("Loaded ~p module on ~p on ~n", [Mod, Nodes, Res]);
+    emqx_ctl:print("Loaded ~p module on ~p: ~p~n", [Module, Nodes, Res]);
 cmd(_) ->
     emqx_ctl:usage([
-        {"observer status", "observer_cli:start()"},
-        {"observer bin_leak", "recon:bin_leak(100)"},
-        {"observer load Mod", "recon:remote_load(Mod) to all nodes"}
+        {"observer status", "Start observer in the current console"},
+        {"observer bin_leak",
+            "Force all processes to perform garbage collection "
+            "and prints the top-100 processes that freed the "
+            "biggest amount of binaries, potentially highlighting leaks."},
+        {"observer load Mod", "Ensure a module is loaded in all EMQX nodes in the cluster"}
     ]).
 
 %% recon:remote_load/1 has a bug, when nodes() returns [], it is

apps/emqx_modules/test/emqx_observer_cli_tests.erl

@@ -0,0 +1,56 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2022 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+
+-module(emqx_observer_cli_tests).
+
+-include_lib("eunit/include/eunit.hrl").
+
+start_observer_cli_test() ->
+    meck:new(observer_cli, [passthrough, no_history, no_link, no_passthrough_cover]),
+    meck:expect(observer_cli, start, fun() -> ok end),
+    try
+        ok = emqx_observer_cli:cmd(["status"])
+    after
+        meck:unload(observer_cli)
+    end.
+
+bin_leak_test() ->
+    ok = emqx_observer_cli:cmd(["bin_leak"]).
+
+load_observer_cli_test() ->
+    ok = emqx_observer_cli:cmd(["load", "lists"]).
+
+unknown_command_test() ->
+    meck_emqx_ctl(),
+    try
+        ok = emqx_observer_cli:cmd(dummy),
+        receive
+            {usage, [_ | _]} -> ok
+        end
+    after
+        unmeck_emqx_ctl()
+    end.
+
+meck_emqx_ctl() ->
+    Pid = self(),
+    meck:new(emqx_ctl, [passthrough, no_history, no_link, no_passthrough_cover]),
+    meck:expect(emqx_ctl, usage, fun(Tuples) ->
+        Pid ! {usage, Tuples},
+        ok
+    end).
+
+unmeck_emqx_ctl() ->
+    meck:unload(emqx_ctl).