+ Test

src/FSharpPlus/Control/Collection.fs

@@ -289,7 +289,11 @@ type GroupBy =
 type ChunkBy =
     static member ChunkBy (x: Id<'T>  , f: 'T->'Key, _: Id<'Key*Id<'T>>    , [<Optional>]_impl: ChunkBy) = let a = Id.run x in Id.create (f a, x)
     static member ChunkBy (x: seq<'T> , f: 'T->'Key, _: seq<'Key*seq<'T>>  , [<Optional>]_impl: ChunkBy) = Seq.chunkBy f x |> Seq.map (fun (x,y) -> x, y :> _ seq)
-    static member ChunkBy (x: list<'T>, f: 'T->'Key, _: list<'Key*list<'T>>, [<Optional>]_impl: ChunkBy) = List.chunkBy f x
+    static member ChunkBy (x: list<'T>, f: 'T->'Key, _: list<'Key*list<'T>>, [<Optional>]_impl: ChunkBy) =
+        #if TEST_TRACE
+        Traces.add "ChunkBy, list<'T>"
+        #endif
+        List.chunkBy f x
     static member ChunkBy (x: 'T []   , f: 'T->'Key, _: ('Key*('T [])) []  , [<Optional>]_impl: ChunkBy) = Seq.chunkBy f x |> Seq.map (fun (x,y) -> x, Seq.toArray y) |> Seq.toArray
 
     static member inline Invoke (projection: 'T->'Key) (source: '``Collection<'T>``) : '``Collection<'Key * 'Collection<'T>>`` = 

tests/FSharpPlus.Tests/Collections.fs

@@ -0,0 +1,24 @@
+namespace FSharpPlus.Tests
+
+open FSharpPlus
+open FSharpPlus.Data
+open NUnit.Framework
+
+#if TEST_TRACE
+open FSharpPlus.Internals
+#endif
+
+module Collections2 =
+
+    [<Test>]    
+    let chunkBy () =
+        #if TEST_TRACE
+        Traces.reset()
+        #endif
+        let source = [1; 2; 3; 5; 7; 9]
+        let expected = [(1, [1]); (0, [2]); (1, [3; 5; 7; 9])]
+        let actual = List.chunkBy (flip (%) 2) source
+        CollectionAssert.AreEqual(expected, actual)
+        #if TEST_TRACE
+        CollectionAssert.AreEqual (["ChunkBy, list<'T>"], Traces.get())
+        #endif

tests/FSharpPlus.Tests/FSharpPlus.Tests.fsproj

@@ -23,6 +23,7 @@
     <Compile Include="Parsing.fs" />
     <Compile Include="Traversals.fs" />
     <Compile Include="Indexables.fs" />
+    <Compile Include="Collections.fs" />
     <Compile Include="Validations.fs" />
     <Compile Include="Task.fs" />
     <Compile Include="ValueTask.fs" />