test_that("Invalid `control`.", {
  expect_error(el_control(maxit = NA))
  expect_error(el_control(maxit = 0.1))
  expect_error(el_control(maxit_l = NA))
  expect_error(el_control(maxit_l = 0.1))
  expect_error(el_control(tol = Inf))
  expect_error(el_control(tol = -1))
  expect_error(el_control(tol_l = Inf))
  expect_error(el_control(tol_l = -1))
  expect_error(el_control(step = Inf))
  expect_error(el_control(step = -1))
  expect_error(el_control(th = Inf))
  expect_error(el_control(th = -10))
  expect_error(el_control(verbose = "TRUE"))
  expect_error(el_control(keep_data = c(TRUE, TRUE)))
  expect_error(el_control(nthreads = c(10, 20)))
  expect_error(el_control(nthreads = 0))
  expect_warning(el_control(nthreads = .Machine$integer.max))
})