test_that("scaled population mad approximately equal to 1 for N(0,1)", {
  expect_equal(round(pop.mad(qnorm, pnorm), 4), 1)
})

test_that("scaled population mad approximately equal to 2 for N(0,4)", {
  expect_equal(round(pop.mad(qnorm, pnorm, sd = 2), 4), 2)
})