test_that("with_deduped(f(x)) runs only on deduplicated values", {
  get_ncalls <- function() as.integer(Sys.getenv("ncalls"))
  increment_ncalls <- function() Sys.setenv(ncalls = get_ncalls() + 1L)

  f <- function(ii) for (i in ii) increment_ncalls()

  withr::with_envvar(
    c(ncalls = 0),
    {
      x <- c(1, 1, 1, 2, 3)
      f(x) |> with_deduped()
      expect_equal(get_ncalls(), 3)
    }
  )

  withr::with_envvar(
    c(ncalls = 0),
    {
      x <- 1:5
      f(x) |> with_deduped()
      expect_equal(get_ncalls(), 5)
    }
  )
})

test_that("with_deduped(f(x, y)) is the same as deduped(f)(x, y)", {
  x <- c(1, 3, 1, 2, 2, 1)
  increment_by_n <- \(x, n) x + n
  inc <- 3
  expect_equal(
    increment_by_n(x, inc) |> with_deduped(),
    deduped(increment_by_n)(x, inc)
  )
})