test_that("get_letters returns right-length lists and vectors", {
  mod <- viztest_chick_model()
  chick_emm <- emmeans::emmeans(mod, "feed")
  chick_gl <- multcomp::glht(mod, linfct=multcomp::mcp(feed="Tukey"))
  cl_em <- get_letters(chick_emm)
  expect_equal(nrow(cl_em), 6)
  expect_equal(ncol(cl_em), 3)
  cl_gl <- get_letters(chick_gl, test = multcomp::adjusted('none'))
  expect_equal(nrow(cl_gl), 6)
  expect_equal(ncol(cl_gl), 4)
})