test_that("mod_nullable", {
  expect_true(mod_nullable(is_all_distinct)(c(1, 3, NA, NA)))
  expect_true(mod_nullable(is_incrementing)(c(1, NA, 3)))
})

test_that("mod_infinitable", {
  x <- c(1, Inf, 3)
  is_incrementing_inf <- mod_infinitable(is_incrementing)
  expect_true(is_incrementing_inf(x))
})