test for ensuring `data_dir` is set correctly in ct configs

this test almost certainly only fails under very limited circumstances
limiting it's utility. it is known to fail with some versions of rebar3
when this test is run via `rebar3 ct --cover`

test/rebar_ct_SUITE.erl

@@ -17,13 +17,15 @@
          multi_suite/1,
          all_suite/1,
          single_dir_and_single_suite/1,
-         symlinked_dir_overwritten_fix/1]).
+         symlinked_dir_overwritten_fix/1,
+         data_dir_correct/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
 all() -> [{group, basic_app},
           {group, multi_app},
-          {group, dirs_and_suites}].
+          {group, dirs_and_suites},
+          {group, data_dirs}].
 
 groups() -> [{basic_app, [], [basic_app_default_dirs,
                               basic_app_default_beams]},
@@ -38,7 +40,8 @@ groups() -> [{basic_app, [], [basic_app_default_dirs,
                                     multi_suite,
                                     all_suite,
                                     single_dir_and_single_suite,
-                                    symlinked_dir_overwritten_fix]}].
+                                    symlinked_dir_overwritten_fix]},
+             {data_dirs, [], [data_dir_correct]}].
 
 init_per_group(basic_app, Config) ->
     C = rebar_test_utils:init_rebar_state(Config, "ct_"),
@@ -139,7 +142,8 @@ init_per_group(dirs_and_suites, Config) ->
     ok = filelib:ensure_dir(Suite3),
     ok = file:write_file(Suite3, test_suite("extras")),
 
-    [{appnames, [Name1, Name2]}|C].
+    [{appnames, [Name1, Name2]}|C];
+init_per_group(_, Config) -> Config.
 
 end_per_group(_Group, _Config) -> ok.
 
@@ -544,7 +548,13 @@ symlinked_dir_overwritten_fix(Config) ->
 
     {ok, _} = rebar_test_utils:run_and_check(Config, [], ["as", "test", "compile"], return).
 
+data_dir_correct(Config) ->
+    DataDir = ?config(data_dir, Config),
+    Parts = filename:split(DataDir),
+    ["rebar_ct_SUITE_data","test","rebar","lib","test","_build"|_] = lists:reverse(Parts).
 
+
+%% helper for generating test data
 test_suite(Name) ->
     io_lib:format("-module(~ts_SUITE).\n"
                   "-compile(export_all).\n"