test_that("fourierdf returns expected structure", {
  set.seed(42)
  y <- cumsum(rnorm(100))
  res <- fourierdf(y)
  expect_s3_class(res, "fourierdf")
  expect_true(is.numeric(res$statistic))
  expect_true(is.finite(res$statistic))
  expect_true(res$k >= 1 && res$k <= 5)
  expect_true(res$p >= 0)
  expect_length(res$cv, 3)
  expect_named(res$cv, c("1%", "5%", "10%"))
  expect_true(res$cv["1%"] < res$cv["5%"])
})

test_that("fouriergls returns expected structure", {
  set.seed(42)
  y <- cumsum(rnorm(100))
  res <- fouriergls(y)
  expect_s3_class(res, "fouriergls")
  expect_true(is.finite(res$statistic))
  expect_true(is.finite(res$cbar))
  expect_length(res$cv, 3)
})

test_that("fourierkpss returns expected structure", {
  set.seed(42)
  y <- cumsum(rnorm(100))
  res <- fourierkpss(y)
  expect_s3_class(res, "fourierkpss")
  expect_true(is.finite(res$statistic))
  expect_true(res$statistic > 0)  # KPSS statistic is always positive
  expect_length(res$cv, 3)
})

test_that("fourierlm returns expected structure", {
  set.seed(42)
  y <- cumsum(rnorm(100))
  res <- fourierlm(y)
  expect_s3_class(res, "fourierlm")
  expect_true(is.finite(res$statistic))
  expect_length(res$cv, 3)
})

test_that("fourierfffff returns expected structure", {
  set.seed(42)
  y <- cumsum(rnorm(100))
  res <- fourierfffff(y)
  expect_s3_class(res, "fourierfffff")
  expect_true(is.finite(res$statistic))
  expect_true(res$kfr >= 0.1 && res$kfr <= 2.0)
  expect_length(res$cv, 3)
})

test_that("print methods produce output without error", {
  set.seed(42)
  y <- cumsum(rnorm(80))
  expect_output(print(fourierdf(y)))
  expect_output(print(fouriergls(y)))
  expect_output(print(fourierkpss(y)))
  expect_output(print(fourierlm(y)))
  expect_output(print(fourierfffff(y)))
})

test_that("model=1 (no trend) works for all tests", {
  set.seed(1)
  y <- cumsum(rnorm(80))
  expect_s3_class(fourierdf(y, model = 1), "fourierdf")
  expect_s3_class(fouriergls(y, model = 1), "fouriergls")
  expect_s3_class(fourierkpss(y, model = 1), "fourierkpss")
  expect_s3_class(fourierfffff(y, model = 1), "fourierfffff")
})

test_that("fourierall runs all 6 tests", {
  set.seed(99)
  y <- cumsum(rnorm(80))
  res <- suppressMessages(fourierall(y))
  expect_named(res, c("lm", "adf", "gls", "kpss", "fffff", "dfdf"))
})

test_that("fourierdfdf returns expected structure", {
  set.seed(42)
  y <- cumsum(rnorm(100))
  res <- fourierdfdf(y)
  expect_s3_class(res, "fourierdfdf")
  expect_true(is.numeric(res$statistic))
  expect_true(res$ks >= 1 && res$ks <= 3)
  expect_true(res$kc >= 1 && res$kc <= 3)
  expect_length(res$cv, 3)
  expect_named(res$cv, c("1%", "5%", "10%"))
  expect_output(print(res))
})

test_that("fourierdfdf bootstrap works", {
  set.seed(7)
  y <- cumsum(rnorm(60))
  res <- fourierdfdf(y, bootstrap = TRUE, breps = 50)
  expect_s3_class(res, "fourierdfdf")
  expect_false(is.null(res$bcv))
  expect_length(res$bcv, 3)
  expect_named(res$bcv, c("1%", "5%", "10%"))
  expect_true(res$bcv["1%"] < res$bcv["5%"])
})