danepitkin commented on code in PR #36768:
URL: https://github.com/apache/arrow/pull/36768#discussion_r1268164338
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python/pyarrow/tests/test_exec_plan.py:
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@@ -321,3 +321,17 @@ def test_join_extension_array_column():
result = _perform_join(
"left outer", t1, ["colB"], t3, ["colC"])
assert result["colB"] == pa.chunked_array(ext_array)
+
+
+def test_group_by_ordering():
+ # GH-36709 - preserve ordering in groupby by setting use_threads=False
+ table1 = pa.table({'a': [1, 2, 3, 4], 'b': ['a'] * 4})
+ table2 = pa.table({'a': [1, 2, 3, 4], 'b': ['b'] * 4})
+ table = pa.concat_tables([table1, table2])
+
+ for _ in range(50):
+ # 50 seems to consistently cause errors when order is not preserved.
+ # If the order problem is reintroduced this test will become flaky
+ # which is still a signal that the order is not preserved.
Review Comment:
I do worry that a flaky test in the future might go unnoticed for awhile.
For example, a developer might just run the test until it "passes" once and
assume the flakiness is unexpected. I don't really see a better way to test
something like this without having control over the Acero execution
environment, though.. This is a good approach given this restraint!
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