test_that("modify_if", {
  x = modify_if(iris, is.factor, as.character)
  expect_character(x$Species)

  x = modify_if(as.data.table(iris), is.factor, as.character)
  expect_character(x$Species)
})

test_that("modify_at", {
  x = modify_at(iris, "Species", as.character)
  expect_character(x$Species)

  x = modify_at(as.data.table(iris), "Species", as.character)
  expect_character(x$Species)
})