test_that("Mathur's AutoDX handles inputs well", {
  expect_error(step.M(sin, 1, range = c(0, 1), cores = 1), "must be a positive vector of length 2")
  expect_warning(step.M(sin, 1, range = c(1e-4, 1e-6), cores = 1), "was extended to")
})

test_that("Mathur's step selection behaves reasonably", {
  s <- step.M(x = pi/4, sin, diagnostics = TRUE, plot = TRUE, cores = 1)
  expect_equal(s$exitcode, 0)
  expect_equal(s$value, sqrt(2)/2, tolerance = 1e-8)
  if (file.exists("Rplot.pdf")) unlink("Rplot.pdf")
})

test_that("Mathur's step returns reasonable values even with bad slopes", {
  expect_warning(m <- step.M(sin, 1, shrink.factor = 0.125, cores = 1), "wrong reduction rate")
  expect_equal(m$exitcode, 2)

  f <- function(x) ifelse(x %in% 1:2, x^2, NA)
  expect_warning(m <- step.M(f, 1, cores = 1), "<3 finite function values")
  expect_equal(m$exitcode, 3)
})

test_that("Parallelisation in Mathur's algorithm works", {
  expect_equal(step.M(sin, 1, cores = 1), step.M(sin, 1, cores = 2))
  clus <- parallel::makePSOCKcluster(2)
  expect_equal(step.M(sin, 1, cores = 1), step.M(sin, 1, cl = clus))
  parallel::stopCluster(clus)

  # Testing a slow function
  # f <- function(x) {Sys.sleep(0.1); sin(x)}
  # system.time(step.M(f, 1))
  # system.time(step.M(f, 1, cores = 12))
})