context("Interpolation and Extrapolation")
test_that("Cubic interpolation can return NaN", {
  xc <- cubic_interpolate(0.9493646, 1.04033, 0.6949782, 0.1898729, 0.8138197,
    0.03981831,
    ignoreWarnings = TRUE
  )
  testthat::expect_true(is.nan(xc))
})