test_that("mergeRegistries", {
  target = makeTestRegistry()
  f = function(.job, x) { if (x %in% c(2, 7)) fs::file_create(fs::path(.job$external.dir, "foo")); x^2 }
  batchMap(f, 1:10, reg = target)

  td = fs::path(target$temp.dir, fs::path_file(fs::file_temp()))
  fs::dir_create(td)
  file.copy(target$file.dir, td, recursive = TRUE)
  file.dir = fs::path(td, fs::path_file(target$file.dir)) # FIXME: dir_copy?
  source = loadRegistry(file.dir, writeable = TRUE, make.default = FALSE)

  submitAndWait(target, data.table(job.id = 1:4, chunk = 1L))
  submitAndWait(source, data.table(job.id = 6:9, chunk = c(1L, 1L, 1L, 2L)))
  expect_data_table(findDone(reg = source), nrow = 4)
  expect_data_table(findDone(reg = target), nrow = 4)

  mergeRegistries(source, target)
  expect_data_table(findDone(reg = source), nrow = 4)
  expect_data_table(findDone(reg = target), nrow = 8)

  checkTables(target)

  expect_set_equal(list.files(dir(target, "external")), as.character(c(2, 7)))
  expect_equal(unwrap(reduceResultsDataTable(reg = target))$result.1, c(1,2,3,4,6,7,8,9)^2)
  expect_file_exists(fs::path(target$file.dir, "external", c("2", "7"), "foo"))

  fs::dir_delete(td)
})