Add tests for prevent silent dropping

src/error_logger_lager_h.erl

@@ -596,3 +596,37 @@ get_value(Key, List, Default) ->
 
 supervisor_name({local, Name}) -> Name;
 supervisor_name(Name) -> Name.
+
+-ifdef(TEST).
+-include_lib("eunit/include/eunit.hrl").
+
+no_silent_hwm_drops_test_() ->
+    {timeout, 10000,
+        [
+            fun() ->
+                error_logger:tty(false),
+                application:load(lager),
+                application:set_env(lager, handlers, [{lager_test_backend, warning}]),
+                application:set_env(lager, error_logger_redirect, true),
+                application:set_env(lager, error_logger_hwm, 5),
+                application:set_env(lager, error_logger_flush_queue, false),
+                application:unset_env(lager, crash_log),
+                lager:start(),
+                try
+                    {_, _, MS} = os:timestamp(),
+                    timer:sleep((1000000 - MS) div 1000 + 1),
+                    %start close to the beginning of a new second
+                    [error_logger:error_msg("Foo ~p~n", [K]) || K <- lists:seq(1, 15)],
+                    timer:sleep(1000),
+                    lager_handler_watcher:pop_until("lager_error_logger_h dropped 10 messages in the last second that exceeded the limit of 5 messages/sec",
+                        fun lists:flatten/1)
+                after
+                    application:stop(lager),
+                    application:stop(goldrush),
+                    error_logger:tty(true)
+                end
+            end
+        ]
+    }.
+
+-endif.

src/lager_file_backend.erl

@@ -957,6 +957,23 @@ filesystem_test_() ->
             ?assert(filelib:is_regular(TestLog0)),
 
             lager_util:delete_test_dir(TestDir)
+        end},
+        {"no silent hwm drops",
+        fun() ->
+            TestDir = lager_util:create_test_dir(),
+            TestLog = filename:join(TestDir, "test.log"),
+            gen_event:add_handler(lager_event, lager_file_backend, [{file, TestLog}, {level, info},
+                {high_water_mark, 5}, {flush_queue, false}, {sync_on, "=warning"}]),
+            {_, _, MS} = os:timestamp(),
+            timer:sleep((1000000 - MS) div 1000 + 1),
+            %start close to the beginning of a new second
+            [lager:log(info, self(), "Foo ~p", [K]) || K <- lists:seq(1, 15)],
+            timer:sleep(1000),
+            {ok, Bin} = file:read_file(TestLog),
+            Last = lists:last(re:split(Bin, "\n", [{return, list}, trim])),
+            ?assertMatch([_, _, _, _, "lager_file_backend dropped 10 messages in the last second that exceeded the limit of 5 messages/sec"],
+                re:split(Last, " ", [{return, list}, {parts, 5}])),
+            lager_util:delete_test_dir(TestDir)
         end}
     ]}.