fix: restore design_stats invalid-design test setup

Author: zankrut20

.Rbuildignore

@@ -25,4 +25,4 @@
 ^\.lintr$
 ^lintr\.R$
 ^.*\.txt$
-^.*\.mhtml$
+^.*\.mhtml$

tests/testthat/test-design_stats.R

@@ -397,7 +397,8 @@ test_that("design_stats_api SPD (design_type=3) returns main-plot error", {
 })
 
 test_that("design_stats_api stops on invalid design_type integer", {
-  skip_on_cran() # error handling test or warning testd <- rcbd_data()
+  skip_on_cran()
+  d <- rcbd_data()
   data_mat <- cbind(d$trait1, d$trait2)
   expect_error(
     selection.index:::design_stats_api(data_mat, d$gen_idx, d$rep_idx,