test_that("fit_isotherm_batch fits each group and returns one row per group", {
  df <- data.frame(
    id = rep(c("A", "B"), each = 6),
    Ce = rep(c(2, 5, 10, 20, 35, 50), 2),
    qe = c(0.8, 1.6, 2.3, 3.0, 3.6, 4.0,
           0.5, 1.0, 1.6, 2.2, 2.7, 3.0)
  )
  res <- fit_isotherm_batch(df, "id", "Ce", "qe", model = "langmuir")
  expect_equal(nrow(res), 2)
  expect_true(all(c("id", "Qmax", "KL", "R2") %in% names(res)))
  expect_true(all(res$R2 > 0.9))
})

test_that("fit_isotherm_batch skips failing groups with a warning", {
  df <- data.frame(
    id = c(rep("A", 6), rep("bad", 2)),
    Ce = c(2, 5, 10, 20, 35, 50, 1, 2),
    qe = c(0.8, 1.6, 2.3, 3.0, 3.6, 4.0, 1, 1)
  )
  expect_warning(res <- fit_isotherm_batch(df, "id", "Ce", "qe", model = "langmuir"),
                  "could not be fit")
  expect_equal(nrow(res), 1)
  expect_equal(res$id, "A")
})

test_that("fit_isotherm_batch errors when no group can be fit", {
  df <- data.frame(id = "only_one", Ce = 5, qe = 1)
  expect_error(suppressWarnings(fit_isotherm_batch(df, "id", "Ce", "qe", model = "langmuir")),
               "No groups")
})

test_that("fit_kinetics_batch fits each group and returns one row per group", {
  df <- data.frame(
    id = rep(c("A", "B"), each = 6),
    t = rep(c(5, 15, 30, 60, 120, 240), 2),
    qt = c(1.2, 2.1, 2.9, 3.6, 4.0, 4.2,
           0.8, 1.5, 2.0, 2.5, 2.8, 3.0)
  )
  res <- fit_kinetics_batch(df, "id", "t", "qt", model = "pso")
  expect_equal(nrow(res), 2)
  expect_true(all(c("id", "qe", "k2", "R2") %in% names(res)))
})

test_that("batch functions error on missing columns", {
  df <- data.frame(id = "A", Ce = 1, qe = 1)
  expect_error(fit_isotherm_batch(df, "id", "Ce", "missing_col", model = "langmuir"),
               "not found")
})