expect_equal_difftime <- function(a, b) {
  expect_equal(as.numeric(a, units = "secs"), as.numeric(b, units = "secs"))
}

test_that("we can retrieve an interval", {
  con <- dbConnect(duckdb())
  on.exit(dbDisconnect(con, shutdown = TRUE))

  res <- dbGetQuery(con, "SELECT '2021-11-26'::TIMESTAMP-'1984-04-24'::TIMESTAMP i")
  expect_equal_difftime(as.Date("2021-11-26") - as.Date("1984-04-24"), res$i)

  res <- dbGetQuery(con, "SELECT '2021-11-26 12:01:00'::TIMESTAMP-'2021-11-26 12:00:00'::TIMESTAMP i")
  expect_equal_difftime(as.POSIXct("2021-11-26 12:01:00") - as.POSIXct("2021-11-26 12:00:00"), res$i)

  res <- dbGetQuery(con, "SELECT '1984-04-24'::TIMESTAMP-'2021-11-26'::TIMESTAMP i")
  expect_equal_difftime(as.Date("1984-04-24") - as.Date("2021-11-26"), res$i)

  res <- dbGetQuery(con, "SELECT '2021-11-26 12:00:00'::TIMESTAMP - '2021-11-26 12:01:00'::TIMESTAMP i")
  expect_equal_difftime(as.POSIXct("2021-11-26 12:00:00") - as.POSIXct("2021-11-26 12:01:00"), res$i)

  res <- dbGetQuery(con, "SELECT NULL::INTERVAL i")
  expect_true(is.na(res$i))
})