test_that("fit_elovich converges and returns sensible R2", {
  t <- c(5, 15, 30, 60, 120, 240)
  qt <- c(1.2, 2.1, 2.9, 3.6, 4.0, 4.2)
  fit <- fit_elovich(t, qt)
  expect_true(fit$R2 > 0.9)
  expect_true(fit$alpha > 0)
})

test_that("fit_intraparticle fits a linear model on sqrt(t)", {
  t <- c(5, 15, 30, 60, 120, 240)
  qt <- c(1.2, 2.1, 2.9, 3.6, 4.0, 4.2)
  fit <- fit_intraparticle(t, qt)
  expect_s3_class(fit$model, "lm")
  expect_true(fit$R2 > 0.7)
})