test_that("diff", {
  expect_equal(
    dtt_diff(as.Date(character(0)), as.Date("2001-01-01")),
    numeric(0)
  )
  expect_equal(dtt_diff(NA_character_, as.Date("2001-01-01")), NA_real_)
  expect_equal(
    dtt_diff(
      as.Date(c("2001-01-02", "2000-12-31")),
      as.Date("2001-01-01"),
      "hours"
    ),
    c(24, -24)
  )
  expect_equal(
    dtt_diff(as.Date("2001-01-02"), as.Date("2001-01-01"), "weeks"),
    1 / 7
  )
  expect_equal(
    dtt_diff(as.POSIXct("2001-01-02"), as.POSIXct("2001-01-01"), "weeks"),
    1 / 7
  )
  expect_equal(
    dtt_diff(
      as.POSIXct("2001-01-01", tz = "Etc/GMT+8"),
      as.POSIXct("2001-01-01", tz = "Etc/GMT+9"),
      "hours"
    ),
    -1
  )
  expect_equal(
    dtt_diff(
      as.POSIXct("2001-01-01 00:01:00", tz = "Etc/GMT+8"),
      as.POSIXct("2001-01-01 00:02:31", tz = "Etc/GMT+9"),
      "mins"
    ),
    -61.5166666666667
  )
})