[GitHub] [arrow] thisisnic commented on a change in pull request #12431: ARROW-14826 [R] Implement bindings for `lubridate::dst()`

[GitBox <gi...@apache.org>]

thisisnic commented on a change in pull request #12431:
URL: https://github.com/apache/arrow/pull/12431#discussion_r811289144



##########
File path: r/tests/testthat/test-dplyr-funcs-datetime.R
##########
@@ -711,3 +711,40 @@ test_that("am/pm mirror lubridate", {
   )
 
 })
+test_that("dst extracts daylight savings time correctly", {
+  test_df <- tibble(
+    dates = as.POSIXct(c("2021-02-20", "2021-07-31", "2021-10-31", "2021-01-31"), tz = "Europe/London")
+  )
+  # https://issues.apache.org/jira/browse/ARROW-13168
+  skip_on_os("windows")
+
+  compare_dplyr_binding(
+    .input %>%
+      mutate(dst = dst(dates)) %>%
+      collect(),
+    test_df
+  )
+})
+
+test_that("dst errors with unsupported input", {
+  expect_error(
+    call_function("is_dst", Scalar$create("this is a string, not a timestamp")),
+    "NotImplemented: Function 'is_dst' has no kernel matching input types (scalar[string])",
+    fixed = TRUE
+  )
+  expect_error(
+    call_function("is_dst", Scalar$create(1L)),
+    "NotImplemented: Function 'is_dst' has no kernel matching input types (scalar[int32])",
+    fixed = TRUE
+  )
+  expect_error(
+    call_function("is_dst", Scalar$create(2.2)),
+    "NotImplemented: Function 'is_dst' has no kernel matching input types (scalar[double])",
+    fixed = TRUE
+  )
+  expect_error(
+    call_function("is_dst", Scalar$create(TRUE)),
+    "NotImplemented: Function 'is_dst' has no kernel matching input types (scalar[bool])",
+    fixed = TRUE
+  )

Review comment:
       I think you make a great point here @dragosmg about consistent error messaging.  I just wonder if the term "kernel" might be unfamiliar to our R users who are less familiar with the C++ underpinnings of the package as well.




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