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Add a test for classifyScan #3216

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harendra-kumar merged 1 commit into from
May 12, 2026
Merged

Add a test for classifyScan #3216

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18 changes: 18 additions & 0 deletions test/Streamly/Test/Data/Fold.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -656,6 +656,23 @@ classify =
Data.Map.fromList
[("ONE",[1.0, 1.1 :: Double]), ("TWO",[2.0, 2.2])]

-- classifyScan emits Just (k, b) each time the per-key fold completes, Nothing
-- otherwise; once a key's fold is done, further values for that key are dropped.
classifyScan :: Expectation
classifyScan =
let getKey = fst
innerFold = Fold.lmap snd (Fold.take 2 Fold.sum)
input = Stream.fromList
[ ("ONE", 1::Int)
, ("TWO", 2)
, ("ONE", 3) -- ONE fold completes: 1+3 = 4
, ("TWO", 4) -- TWO fold completes: 2+4 = 6
, ("ONE", 5) -- ONE already done, dropped
]
in Stream.fold Fold.toList
(Stream.postscanlMaybe (Fold.classifyScan getKey innerFold) input)
`shouldReturn` [("ONE", 4), ("TWO", 6)]

splitAt :: Expectation
splitAt =
Stream.fold
Expand Down Expand Up @@ -739,6 +756,7 @@ main = hspec $ do
prop "demuxWith" demuxWith
prop "classifyWith" classifyWith
prop "classify" classify
prop "classifyScan" classifyScan

-- Terminating folds
prop "index" index
Expand Down
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