tests/testthat/test-boxcox.R

In forecast: Forecasting Functions for Time Series and Linear Models

# A unit test for boxcox transformations
if (require(testthat)) {
  test_that("tests for biasadj automatically set based on model fit", {
    # lm
    fit <- tslm(USAccDeaths ~ trend, lambda = 0.5, biasadj = TRUE)
    expect_true(all.equal(forecast(fit), forecast(fit, biasadj = TRUE)))

    # HoltWintersZZ
    fit <- ses(USAccDeaths, initial = "simple", lambda = 0.5, biasadj = TRUE)
    expect_true(all.equal(forecast(fit), forecast(fit, biasadj = TRUE)))

    # arfima
    x <- fracdiff::fracdiff.sim(100, ma = -.4, d = .3)$series
    fit <- arfima(x)
    expect_true(all.equal(forecast(fit), forecast(fit, biasadj=TRUE)))

    #arima
    fit1 <- Arima(USAccDeaths, order = c(0,1,1), seasonal = c(0,1,1), lambda = 0.5, biasadj = TRUE)
    fit2 <- auto.arima(USAccDeaths, max.p=0, max.d=1, max.q=1, max.P=0, max.D=1, max.Q=1, lambda = 0.5, biasadj = TRUE)
    expect_true(all.equal(forecast(fit1), forecast(fit1, biasadj=TRUE)))
    expect_true(all.equal(forecast(fit2), forecast(fit2, biasadj=TRUE)))
    expect_true(all.equal(forecast(fit1)$mean, forecast(fit2)$mean))

    # ets
    fit <- ets(USAccDeaths, model = "ANA", lambda = 0.5, biasadj = TRUE)
    expect_true(all.equal(forecast(fit), forecast(fit, biasadj = TRUE)))

    # bats
    # fit <- bats(USAccDeaths, use.box.cox = TRUE, biasadj = TRUE)
    # expect_true(all.equal(forecast(fit), forecast(fit, biasadj=TRUE)))

    # tbats
    # fit <- tbats(USAccDeaths, use.box.cox = TRUE, biasadj = TRUE)
    # expect_true(all.equal(forecast(fit), forecast(fit, biasadj=TRUE)))
  })

  test_that("tests for automatic lambda selection in BoxCox transformation", {
    lambda_auto <- BoxCox.lambda(USAccDeaths)

    # lm
    fit <- tslm(USAccDeaths ~ trend, lambda = "auto", biasadj = TRUE)
    expect_equal(as.numeric(fit$lambda), lambda_auto, tolerance=1e-3)

    # ets
    fit <- ets(USAccDeaths, model = "ANA", lambda = "auto", biasadj = TRUE)
    expect_equal(as.numeric(fit$lambda), lambda_auto, tolerance=1e-3)

    # arima
    fit <- Arima(USAccDeaths, order = c(0,1,1), seasonal = c(0,1,1), lambda = "auto", biasadj = TRUE)
    expect_equal(as.numeric(fit$lambda), lambda_auto, tolerance=1e-3)
  })
}