test_that("DataBackendRename", {
  old = names(iris)
  new = paste0("xx_", old)
  b1 = as_data_backend(iris)
  b = DataBackendRename$new(b1, old, new)
  expect_backend(b)

  expect_set_equal(b$colnames, c(new, "..row_id"))
  expect_set_equal(names(b$data(b$rownames, b$colnames)), c(new, "..row_id"))
  expect_set_equal(names(b$head()), c(new, "..row_id"))

  expect_data_table(b$data(rows = b$rownames, cols = old), ncols = 0)
  expect_data_table(b$data(rows = b$rownames, cols = new), ncols = 5)

  expect_equal(unname(b1$col_hashes), unname(b$col_hashes))

})

test_that("DataBackendRename / partial rename", {
  old = names(iris)[1:2]
  new = paste0("xx_", old)
  b1 = as_data_backend(iris)
  b = DataBackendRename$new(b1, old, new)
  expect_backend(b)

  expected = c(map_values(names(iris), old, new), "..row_id")
  expect_set_equal(b$colnames, expected)

  expect_set_equal(names(b$data(b$rownames, b$colnames)), expected)
  expect_set_equal(names(b$head()), expected)

  expect_data_table(b$data(rows = b$rownames, cols = expected), ncols = 6)

  expect_equal(unname(b1$col_hashes), unname(b$col_hashes))

})

test_that("nested backends", {
  data = as.data.table(iris)
  b1 = as_data_backend(data)
  b2 = DataBackendRename$new(as_data_backend(data), old = names(iris), new = paste0("new_", names(iris)))
  b = DataBackendCbind$new(b1, b2)
  expect_backend(b1)
  expect_backend(b2)
  expect_backend(b)

  expect_set_equal(b$rownames, 1:150)
  expect_set_equal(b$colnames, c(b1$colnames, b2$colnames))


  expect_equal(b$col_hashes, c(b1$col_hashes, b2$col_hashes)[setdiff(b$colnames, b$primary_key)])

  expect_set_equal(b$col_hashes, b1$col_hashes)  # b2 has the same hashes, so cbind should have duplicate hashes.

})

test_that("rename does not yield duplicated columns (#701)", {
  db = DataBackendDataTable$new(data.table(id = 1L, a = 1, b = 2), primary_key = "id")
  expect_error(DataBackendRename$new(db, "a", "b"), "duplicated", ignore.case = TRUE)
})