test_that("timeS parameter", {
  expect_error(forecast("a", h = 12), "timeS parameter should be of class ts or a numeric vector")
  expect_no_error(forecast(1:36, lags = 1:2, h = 12))
  expect_no_error(forecast(AirPassengers, h = 12))
})

test_that("h parameter", {
  expect_error(forecast(AirPassengers, h = "a"), "h parameter should be an integer scalar value >= 1")
  expect_error(forecast(AirPassengers, h = 1:2), "h parameter should be an integer scalar value >= 1")
})

test_that("lags parameter", {
  expect_error(forecast(AirPassengers, h = 12, lags = "a"), "lags parameter should be NULL or numeric")
  expect_error(forecast(AirPassengers, h = 12, lags = 3:1), "lags should be a vector in increasing order")
})

# test_that("External model works as embebed model", {
#   bm <- function(X, y) {
#     structure(list(X = X, y = y), class = "my_knn")
#   }
#   predict.my_knn <- function(object, example) {
#     FNN::knn.reg(train = object$X, test = example, y = object$y)$pred
#   }
#   f <- forecast(AirPassengers, h = 12, method = bm)
#   f2 <- forecast(AirPassengers, h = 12, method = "knn")
#   expect_equal(f$pred, f2$pred)
# })