test_that("plot_trend retorna ggplot com linhas de tendencia", {
  skip_on_cran()  # opcional: evita flutuar por ruido aleatorio em CI
  set.seed(1)
  df <- data.frame(
    data = as.Date("2024-01-01") + 0:11*30,
    rio = rep(c("R1","R1","R1"), 4)[1:12],
    ponto = "P1",
    turbidez = 20 + (-0.4)*(0:11) + rnorm(12, 0, 0.6)
  )
  g1 <- plot_trend(df, param = "turbidez", method = "theilsen")
  g2 <- plot_trend(df, param = "turbidez", method = "ols")
  g3 <- plot_trend(df, param = "turbidez", method = "loess")
  expect_true(inherits(g1, "ggplot"))
  expect_true(inherits(g2, "ggplot"))
  expect_true(inherits(g3, "ggplot"))
})