test_that("Confidence Interval", {
  set.seed(1234)
  X <- cbind(
    generate_brownian_motion(200, v = seq(0, 1, 0.05))$data,
    generate_brownian_motion(100, v = seq(0, 1, 0.05))$data + 0.1,
    generate_brownian_motion(150, v = seq(0, 1, 0.05))$data - 0.05
  )
  res <- confidence_interval(X, c(200, 300))
  expect_equal(res$change, c(200, 300))
  expect_equal(round(res$lower, 4), c(37.5143, 237.1052))
  expect_equal(round(res$upper, 4), c(382.2948, 370.5625))

  expect_error(confidence_interval(X, c()))
  expect_error(confidence_interval(X, c(0)))
})