heights_diff_summary <- heights %>%
  features(year, feat_diff_summary)

test_that("feat_diff_summary returns the right names", {
  expect_equal(
    names(heights_diff_summary),
    c(
      "country",
      "diff_min",
      "diff_q25",
      "diff_median",
      "diff_mean",
      "diff_q75",
      "diff_max",
      "diff_var",
      "diff_sd",
      "diff_iqr"
    )
  )
})

test_that("feat_diff_summary returns the right dimensions", {
  expect_equal(dim(heights_diff_summary), c(144, 10))
})

test_that("feat_diff_summary returns all ids", {
  expect_equal(dplyr::n_distinct(heights_diff_summary$country), 144)
})