ianmcook commented on a change in pull request #9999:
URL: https://github.com/apache/arrow/pull/9999#discussion_r626893022
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File path: r/tests/testthat/test-dplyr-mutate.R
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@@ -15,6 +15,25 @@
# specific language governing permissions and limitations
# under the License.
+# developer note:
+# when adapting tests from the dplyr package, note that expect_dplyr_equal()
+# works differently from expect_equal(). the first argument is a dplyr
+# expression containing the placeholder `input`, and the second argument
+# is the R data frame to pass in as that input. So for example, adapt a test
+# from dplyr as follows:
+#
+# dplyr:
+# expect_equal(
+# mutate(data.frame(x = 1, y = 1), z = 1, x = NULL, y = NULL),
+# data.frame(z = 1)
+# )
+#
+# arrow:
+# expect_dplyr_equal(
+# input %>% mutate(z = 1, x = NULL, y = NULL) %>% collect(),
+# data.frame(x = 1, y = 1)
+# )
Review comment:
Good idea; that would probably be a better place to put this "developer
note" comment
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