test_that("cdm_sample works", {
  con <- DBI::dbConnect(duckdb::duckdb(), eunomia_dir())
  cdm <- cdm_from_con(con, "main", "main")
  cdm_sampled <- cdm_sample(cdm, n = 10)

  df <- cdm_sampled$person %>%
    dplyr::tally() %>%
    dplyr::collect()

  expect_equal(as.double(df$n), 10)

  DBI::dbDisconnect(con, shutdown = TRUE)
})

test_that("cdm_reference assign and unassign", {
  # if I have a class cdm_reference and I access to one element it will have a
  # cdm_reference as attribute
  x <- list(a = 1, b = 2)
  class(x) <- "cdm_reference"
  expect_true("cdm_reference" %in% names(attributes(x[["a"]])))
  expect_true("cdm_reference" %in% names(attributes(x$a)))

  # if I do it for an object that it is not a cdm_reference it wont
  xu <- unclass(x)
  expect_false("cdm_reference" %in% names(attributes(xu[["a"]])))
  expect_false("cdm_reference" %in% names(attributes(xu$a)))

  # I define an element with a cdm reference on it
  xx <- 3
  attr(xx, "cdm_reference") <- 4
  expect_true("cdm_reference" %in% names(attributes(xx)))

  # if I assign this element to a list with no class the attribute will persist
  xu$c <- xx
  expect_true("cdm_reference" %in% names(attributes(xu[["c"]])))
  expect_true("cdm_reference" %in% names(attributes(xu$c)))

  # if I assign to a cdm_reference it wont but it will appear back when I access
  # to one of the elements
  x$c <- xx
  expect_true("cdm_reference" %in% names(attributes(x[["c"]])))
  expect_true("cdm_reference" %in% names(attributes(x$c)))

  # but if after assigning I remove the class the attribute wont be there
  # because when I assigned it was eliminated
  xuu <- unclass(x)
  expect_false("cdm_reference" %in% names(attributes(xuu[["c"]])))
  expect_false("cdm_reference" %in% names(attributes(xuu$c)))
})