test_that("multiplication works", {
  expect_equal(2 * 2, 4)
})

test_that("plot_response returns a ggplot object", {
  Q <- sim_qmatrix(5, 3)
  alpha <- sim_students(10, 3)
  Y <- sim_response(Q, alpha, slip = rep(0.1, 5), guess = rep(0.2, 5))
  p <- plot_response(Y)
  expect_s3_class(p, "ggplot")
})