add a link to the docs about `test_spec` and `cover` in ct warnings

src/rebar_prv_common_test.erl

@@ -165,9 +165,9 @@ cfgopts(State) ->
 
 ensure_opts([], Acc) -> lists:reverse(Acc);
 ensure_opts([{test_spec, _}|_Rest], _Acc) ->
-    ?PRV_ERROR({badconfig, "Test specs not supported"});
+    ?PRV_ERROR({badconfig, "Test specs not supported. See http://www.rebar3.org/docs/running-tests#common-test"});
 ensure_opts([{cover, _}|_Rest], _Acc) ->
-    ?PRV_ERROR({badconfig, "Cover specs not supported"});
+    ?PRV_ERROR({badconfig, "Cover specs not supported. See http://www.rebar3.org/docs/running-tests#common-test"});
 ensure_opts([{auto_compile, _}|_Rest], _Acc) ->
     ?PRV_ERROR({badconfig, "Auto compile not supported"});
 ensure_opts([{suite, Suite}|Rest], Acc) when is_integer(hd(Suite)) ->

test/rebar_ct_SUITE.erl

@@ -1027,7 +1027,7 @@ cfg_test_spec(Config) ->
 
     {error, {rebar_prv_common_test, Error}} = rebar_prv_common_test:prepare_tests(State),
 
-    {badconfig, "Test specs not supported"} = Error.
+    {badconfig, "Test specs not supported. See http://www.rebar3.org/docs/running-tests#common-test"} = Error.
 
 cfg_cover_spec(Config) ->
     C = rebar_test_utils:init_rebar_state(Config, "ct_cfg_cover_spec_opts_"),
@@ -1044,7 +1044,7 @@ cfg_cover_spec(Config) ->
 
     {error, {rebar_prv_common_test, Error}} = rebar_prv_common_test:prepare_tests(State),
 
-    {badconfig, "Cover specs not supported"} = Error.
+    {badconfig, "Cover specs not supported. See http://www.rebar3.org/docs/running-tests#common-test"} = Error.
 
 cfg_atom_suites(Config) ->
     C = rebar_test_utils:init_rebar_state(Config, "ct_cfg_atom_suites_"),