test_that("ci_twinposi returns valid structure", {
  set.seed(1)
  n <- 100
  p <- 30
  X <- matrix(rnorm(n * p), n, p)
  beta <- rep(0, p)
  beta[1:3] <- 1
  y <- X %*% beta + rnorm(n)
  X <- scale(X)

  out <- ci_twinposi(X, y, q = 0.1, boot_rep = 5L, improve_rep = 2L)

  expect_type(out, "list")
  expect_named(out, c("CI_upper", "CI_lower", "selected_index", "beta_star"))
  expect_length(out$selected_index, length(out$CI_upper))
  expect_length(out$selected_index, length(out$CI_lower))
  expect_true(all(out$CI_upper >= out$CI_lower))
  expect_length(out$beta_star, p)
})