jonkeane commented on a change in pull request #11552:
URL: https://github.com/apache/arrow/pull/11552#discussion_r737498949



##########
File path: r/tests/testthat/test-dataset-write.R
##########
@@ -139,6 +139,46 @@ test_that("Writing a dataset: Parquet->Parquet (default)", 
{
   )
 })
 
+test_that("Writing a dataset: existing data behavior", {
+  # This test does not work on Windows because unlink does not immediately
+  # delete the data.
+  skip_on_os("windows")
+  ds <- open_dataset(csv_dir, partitioning = "part", format = "csv")
+  dst_dir <- make_temp_dir()
+  write_dataset(ds, dst_dir, format = "feather", partitioning = "int")
+  expect_true(dir.exists(dst_dir))
+
+  check_dataset <- function() {
+    new_ds <- open_dataset(dst_dir, format = "feather")
+
+    expect_equal(
+      new_ds %>%
+        select(string = chr, integer = int) %>%
+        filter(integer > 6 & integer < 11) %>%
+        collect() %>%
+        summarize(mean = mean(integer)),
+      df1 %>%
+        select(string = chr, integer = int) %>%
+        filter(integer > 6) %>%
+        summarize(mean = mean(integer))
+    )
+  }
+
+  check_dataset()
+  # By default we should overwrite
+  write_dataset(ds, dst_dir, format = "feather", partitioning = "int")
+  check_dataset()
+  write_dataset(ds, dst_dir, format = "feather", partitioning = "int", 
existing_data_behavior = "overwrite")
+  check_dataset()
+  expect_error(
+    write_dataset(ds, dst_dir, format = "feather", partitioning = "int", 
existing_data_behavior = "error"), 

Review comment:
       ```suggestion
       write_dataset(ds, dst_dir, format = "feather", partitioning = "int", 
existing_data_behavior = "error"),
   ```




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