Make sink name construction common & test

Based on code review comments put this function into util.
Added a couple simple unit tests for sanity checking purposes.

src/lager_app.erl

@@ -164,16 +164,9 @@ wrap_proplist_value(undefined) ->
 wrap_proplist_value(Value) ->
     {ok, Value}.
 
-%% The default sink has always been lager_event. Using 'lager_lager_event' is likely to break
-%% historical code and lots of tests.
-make_internal_sink_name(lager) -> ?DEFAULT_SINK;
-
-make_internal_sink_name(Sink) ->
-    list_to_atom(atom_to_list(Sink) ++ "_lager_event").
-
 configure_sink(Sink, SinkDef) ->
     lager_config:new_sink(Sink),
-    ChildId = make_internal_sink_name(Sink),
+    ChildId = lager_util:make_internal_sink_name(Sink),
     _ = supervisor:start_child(lager_sup,
                                {ChildId,
                                 {gen_event, start_link,

src/lager_transform.erl

@@ -79,13 +79,6 @@ walk_body(Acc, []) ->
 walk_body(Acc, [H|T]) ->
     walk_body([transform_statement(H, get(sinks))|Acc], T).
 
-%% 'lager' is special cased because its sink has *always* been named 'lager_event'
-make_internal_sink_name(lager) -> ?DEFAULT_SINK;
-
-%% Everything else should be Sink++_lager_event
-make_internal_sink_name(Sink) ->
-    list_to_atom(atom_to_list(Sink) ++ "_lager_event").
-
 transform_statement({call, Line, {remote, _Line1, {atom, _Line2, Module},
                                   {atom, _Line3, Function}}, Arguments0} = Stmt,
                     Sinks) ->
@@ -93,12 +86,12 @@ transform_statement({call, Line, {remote, _Line1, {atom, _Line2, Module},
         true ->
             case lists:member(Function, ?LEVELS) of
                 true ->
-                    SinkName = make_internal_sink_name(Module),
+                    SinkName = lager_util:make_internal_sink_name(Module),
                     do_transform(Line, SinkName, Function, Arguments0);
                 false ->
                     case lists:keyfind(Function, 1, ?LEVELS_UNSAFE) of
                         {Function, Severity} ->
-                            SinkName = make_internal_sink_name(Module),
+                            SinkName = lager_util:make_internal_sink_name(Module),
                             do_transform(Line, SinkName, Severity, Arguments0, unsafe);
                         false ->
                             Stmt

src/lager_util.erl

@@ -23,7 +23,7 @@
         open_logfile/2, ensure_logfile/4, rotate_logfile/2, format_time/0, format_time/1,
         localtime_ms/0, localtime_ms/1, maybe_utc/1, parse_rotation_date_spec/1,
         calculate_next_rotation/1, validate_trace/1, check_traces/4, is_loggable/3,
-        trace_filter/1, trace_filter/2, expand_path/1, check_hwm/1]).
+        trace_filter/1, trace_filter/2, expand_path/1, check_hwm/1, make_internal_sink_name/1]).
 
 -ifdef(TEST).
 -include_lib("eunit/include/eunit.hrl").
@@ -524,6 +524,14 @@ discard_messages(Second, Count) ->
             Count
     end.
 
+%% @private Build an atom for the gen_event process based on a sink name.
+%% For historical reasons, the default gen_event process for lager itself is named
+%% `lager_event'. For all other sinks, it is SinkName++`_lager_event'
+make_internal_sink_name(lager) ->
+    ?DEFAULT_SINK;
+make_internal_sink_name(Sink) ->
+    list_to_atom(atom_to_list(Sink) ++ "_lager_event").
+
 -ifdef(TEST).
 
 parse_test() ->
@@ -781,4 +789,10 @@ expand_path_test() ->
     end,
     ok.
 
+sink_name_test_() ->
+    [
+        ?_assertEqual(lager_event, make_internal_sink_name(lager)),
+        ?_assertEqual(audit_lager_event, make_internal_sink_name(audit))
+    ].
+
 -endif.