test_that("check_files works", {
  expect_identical(check_files(character(0)), character(0))
  expect_invisible(check_files(character(0)))
  expect_identical(
    check_files(character(0), exists = TRUE),
    check_files(character(0), exists = TRUE)
  )
  expect_invisible(check_files(character(0), exists = TRUE))

  tmp <- withr::local_tempfile()
  expect_identical(check_files(tmp, exists = FALSE), check_files(tmp, exists = FALSE))
  expect_invisible(check_files(tmp, exists = FALSE))
  writeLines(tmp, text = "some test data")
  expect_identical(check_files(tmp, exists = TRUE), check_files(tmp, exists = TRUE))
  expect_invisible(check_files(tmp, exists = TRUE))
})

test_that("check_files errors", {
  expect_chk_error(check_files(NA_character_))

  tmp <- withr::local_tempfile()
  expect_chk_error(
    check_files(tmp),
    "^`tmp` must specify existing files [(]'.*' can't be found[)][.]$"
  )
  expect_chk_error(
    check_files(tempdir()),
    "^`tempdir[(][)]` must specify files [(]'.*' is a directory[)][.]$"
  )
  expect_chk_error(
    check_files(tempdir(), exists = FALSE),
    "^`tempdir[(][)]` must specify files [(]'.*' is a directory[)][.]$"
  )
  writeLines(tmp, text = "some test data")
  expect_chk_error(
    check_files(tmp, exists = FALSE),
    "^`tmp` must not specify existing files [(]'.*' exists[)][.]$"
  )
})