test_that("Gramacy & Lee function example works", {
  gramacy_lee <- function(x) {
    stopifnot(is.numeric(x))
    stopifnot(length(x) == 1)
    f <- expression(sin(10 * pi * x) / (2 * x) + (x - 1)^4)
    g <- D(f, "x")
    h <- D(g, "x")
    f <- eval(f)
    g <- eval(g)
    h <- eval(h)
    list(value = f, gradient = g, hessian = as.matrix(h))
  }
  expect_snapshot(vntrs(f = gramacy_lee, npar = 1, seed = 1))
})

test_that("Shubert function example works", {
  shubert <- function(x) {
    stopifnot(is.numeric(x))
    stopifnot(length(x) == 2)
    f <- expression(
      (cos(2 * x1 + 1) + 2 * cos(3 * x1 + 2) + 3 * cos(4 * x1 + 3) + 4 * cos(5 * x1 + 4) +
        5 * cos(6 * x1 + 5)) *
        (cos(2 * x2 + 1) + 2 * cos(3 * x2 + 2) + 3 * cos(4 * x2 + 3) + 4 * cos(5 * x2 + 4) +
          5 * cos(6 * x2 + 5))
    )
    g1 <- D(f, "x1")
    g2 <- D(f, "x2")
    h11 <- D(g1, "x1")
    h12 <- D(g1, "x2")
    h22 <- D(g2, "x2")
    x1 <- x[1]
    x2 <- x[2]
    f <- eval(f)
    g <- c(eval(g1), eval(g2))
    h <- rbind(c(eval(h11), eval(h12)), c(eval(h12), eval(h22)))
    list(value = f, gradient = g, hessian = h)
  }
  expect_snapshot(vntrs(f = shubert, npar = 2, seed = 1))
})

test_that("Rosenbrock function example works", {
  rosenbrock <- function(x) {
    stopifnot(is.numeric(x))
    stopifnot(length(x) == 2)
    f <- expression(100 * (x2 - x1^2)^2 + (1 - x1)^2)
    g1 <- D(f, "x1")
    g2 <- D(f, "x2")
    h11 <- D(g1, "x1")
    h12 <- D(g1, "x2")
    h22 <- D(g2, "x2")
    x1 <- x[1]
    x2 <- x[2]
    f <- eval(f)
    g <- c(eval(g1), eval(g2))
    h <- rbind(c(eval(h11), eval(h12)), c(eval(h12), eval(h22)))
    list(value = f, gradient = g, hessian = h)
  }
  expect_snapshot(vntrs(f = rosenbrock, npar = 2, seed = 1))
})