test_that("publication_year() works", {
  expect_equal(publication_year(iris_dataset), as.character(1935))
  expect_warning(publication_year(iris_dataset, overwrite=F) <- 1934)
  })


test_that("publication_year() <- assignment works", {
  iris_dataset_2 <- iris_dataset
  publication_year(iris_dataset_2, overwrite=T) <- 1936
  expect_equal(publication_year(iris_dataset_2), as.character(1936))
})

test_that("publication_year()<- NULL results in :unas", {
  iris_dataset_2 <- iris_dataset
  publication_year(iris_dataset_2, overwrite=T) <- NULL
  expect_equal(publication_year(x=iris_dataset_2), ":unas")
})