skip_if_not_installed("lme4")

data(sleepstudy, package = "lme4")
d <- sleepstudy
set.seed(12345)
d$grp <- sample(1:5, size = 180, replace = TRUE)
d$subgrp <- NA
for (i in 1:5) {
  filter_group <- d$grp == i
  d$subgrp[filter_group] <-
    sample(1:30, size = sum(filter_group), replace = TRUE)
}
dd <<- d
model <- lme4::lmer(
  Reaction ~ Days + (1 | grp / subgrp) + (1 | Subject),
  data = dd
)

test_that("n_grouplevels", {
  out <- n_grouplevels(model)
  expect_identical(out$Group, c("subgrp", "grp", "Subject", "subgrp:grp"))
  expect_identical(out$N_levels, c(30L, 5L, 18L, 108L))
})