test_that("Visualization and TTT plot functions work without error", {
  data(burr_data)
  
  # plot_bivteissier
  pdf(tempfile(fileext = ".pdf"))
  on.exit(dev.off())
  
  expect_silent(plot_bivteissier(xi1 = 2, xi2 = 1.5, delta = 0.6, type = "pdf", plot.type = "persp"))
  expect_silent(plot_bivteissier(xi1 = 2, xi2 = 1.5, delta = 0.6, type = "cdf", plot.type = "contour"))
  expect_silent(plot_bivteissier(xi1 = 2, xi2 = 1.5, delta = 0.6, type = "survival", plot.type = "contour"))
  expect_silent(plot_bivteissier(xi1 = 2, xi2 = 1.5, delta = 0.6, type = "hazard", plot.type = "persp"))
  expect_silent(plot_bivteissier(xi1 = 2, xi2 = 1.5, delta = 0.6, type = "rhf", plot.type = "contour"))
  expect_silent(plot_bivteissier(xi1 = 2, xi2 = 1.5, delta = 0.6, type = "locdep", plot.type = "contour"))
  
  # ttt_plot
  expect_silent(ttt_res <- ttt_plot(burr_data))
  expect_true(is.list(ttt_res))
  expect_true("Z1" %in% names(ttt_res))
  expect_true("Z2" %in% names(ttt_res))
  
  # S3 plot methods
  fit_mle <- mlebivteissier(burr_data)
  expect_silent(plot(fit_mle))
  
  set.seed(42)
  fit_bayes <- bayesbivteissier(burr_data, n.iter = 500, burn.in = 100)
  expect_silent(plot(fit_bayes, type = "trace"))
  expect_silent(plot(fit_bayes, type = "density"))
  expect_silent(plot(fit_bayes, type = "autocorr"))
})