test_that("iso", {
  dec25 <- as_iso(gregorian_date(2025, 12, 1:31))
  expect_equal(week_of_year(dec25), granularity(dec25, "week"))
  expect_equal(
    day_of_year(dec25)[1:28],
    day_of_year(as_gregorian(dec25))[1:28] + 2
  )
})