Fix tests without resorting to elvis in rebar.config

(this way we use the default we've defined internally)

elvis.config

@@ -0,0 +1 @@
+[].

src/rebar3_lint.erl

@@ -18,4 +18,4 @@ init(State) ->
 -spec main([]) -> ok | {fail, [elvis_result:file()]}.
 main([]) ->
     ok = application:load(elvis_core),
-    elvis_core:rock(elvis_config:from_rebar("rebar.config")).
+    elvis_core:rock(rebar3_lint_prv:default_config()).

src/rebar3_lint_prv.erl

@@ -1,6 +1,7 @@
 -module('rebar3_lint_prv').
 
 -export([init/1, do/1, format_error/1]).
+-export([default_config/0]).
 
 -ignore_xref([do/1]).
 -ignore_xref([format_error/1]).
@@ -80,7 +81,9 @@ try_elvis_config_file(State) ->
     Filename = filename:join(rebar_dir:root_dir(State), "elvis.config"),
     rebar_api:debug("Looking for Elvis in ~s", [Filename]),
     try elvis_config:from_file(Filename) of
-        [] -> default_config();
+        [] ->
+            rebar_api:debug("Using default Elvis configuration", []),
+            default_config();
         Config -> Config
     catch
         throw:Error ->
@@ -90,7 +93,6 @@ try_elvis_config_file(State) ->
 
 -spec default_config() -> elvis_config:configs().
 default_config() ->
-    rebar_api:debug("Using default Elvis configuration", []),
     [#{ dirs => ["apps/*/src/**", "src/**"],
         filter => "*.erl",
         ruleset => erl_files },

test/test_app_SUITE.erl

@@ -1,11 +1,19 @@
 -module(test_app_SUITE).
 
--export([all/0, test_app/1]).
+-export([init_per_suite/1, end_per_suite/1, all/0, test_app/1]).
 
 -if(?OTP_RELEASE >= 23).
 -behaviour(ct_suite).
 -endif.
 
+init_per_suite(Config) ->
+    RebarState = rebar_state:new(),
+    rebar_state:set(RebarState, elvis, rebar3_lint_prv:default_config()),
+    Config.
+
+end_per_suite(Config) ->
+    Config.
+
 all() ->
     [test_app].