test_that("works", {
  dt <- lazy_dt(data.table(x = 1, y = 1, z = 1), "DT")

  expect_equal(
    dt %>% transmute(x) %>% collect(),
    dt %>% mutate(x, .keep = "none") %>% collect()
  )
})

test_that("empty dots preserves groups", {
  dt <- lazy_dt(data.table(x = 1, y = 1, z = 1), "DT") %>%
    group_by(y)

  res <- dt %>% transmute() %>% collect()

  expect_equal(names(res), "y")
})

test_that("preserves column order", {
  dt <- lazy_dt(data.table(x = 1, y = 1), "DT")

  res <- dt %>% transmute(y, x) %>% collect()

  expect_equal(names(res), c("y", "x"))
})

test_that("works correctly when column is both added and removed in the same call", {
  dt <- lazy_dt(data.table(x = 1, y = 2), "DT")

  res <- dt %>% transmute(y, z = 3, z = NULL) %>% collect()

  expect_equal(names(res), "y")
})