[Repo Assist] test: add SideEffects module to TaskSeq.Using.Tests.fs

release-notes.txt

@@ -2,6 +2,7 @@
 Release notes:
 
 Unreleased
+    - test: add SideEffects module to TaskSeq.Using.Tests.fs; 7 new tests verify Dispose/DisposeAsync call counts, re-iteration semantics, and early-termination disposal for use and use! CE bindings
     - perf: pairwise, distinctUntilChanged, distinctUntilChangedWith, distinctUntilChangedWithAsync now use explicit enumerator + while! instead of ValueOption tracking + for-in loop, eliminating per-element struct match overhead
     - test: add SideEffects module to TaskSeq.Unfold.Tests.fs, verifying generator call counts, re-iteration behaviour, early-termination via take, and exception propagation
     - test: add SideEffects module to TaskSeq.OfXXX.Tests.fs documenting re-iteration semantics (ofSeq re-evaluates source, ofTaskArray re-awaits cached tasks)

src/FSharp.Control.TaskSeq.Test/TaskSeq.Using.Tests.fs

@@ -32,6 +32,18 @@ type private MultiDispose(disposed: int ref) =
     interface IAsyncDisposable with
         member _.DisposeAsync() = ValueTask(task { do disposed.Value <- -1 })
 
+/// Tracks how many times Dispose/DisposeAsync has been called.
+type private CountingDisposable(disposeCount: int ref) =
+    interface IDisposable with
+        member _.Dispose() = disposeCount.Value <- disposeCount.Value + 1
+
+/// Tracks how many times DisposeAsync has been called.
+type private CountingAsyncDisposable(disposeCount: int ref) =
+    interface IAsyncDisposable with
+        member _.DisposeAsync() =
+            disposeCount.Value <- disposeCount.Value + 1
+            ValueTask.CompletedTask
+
 let private check = TaskSeq.length >> Task.map (should equal 1)
 
 [<Fact>]
@@ -105,3 +117,109 @@ let ``CE taskSeq: Using! when type implements IDisposable and IAsyncDisposable``
 
     check ts
     |> Task.map (fun _ -> disposed.Value |> should equal -1) // should prefer IAsyncDisposable, which returns -1
+
+module SideEffects =
+    [<Fact>]
+    let ``CE taskSeq: use - Dispose called exactly once per full iteration`` () = task {
+        let disposeCount = ref 0
+
+        let ts = taskSeq {
+            use _ = new CountingDisposable(disposeCount)
+            yield 1
+        }
+
+        do! ts |> TaskSeq.iter ignore
+        disposeCount.Value |> should equal 1
+    }
+
+    [<Fact>]
+    let ``CE taskSeq: use - Dispose called on each re-iteration`` () = task {
+        let disposeCount = ref 0
+
+        let ts = taskSeq {
+            use _ = new CountingDisposable(disposeCount)
+            yield 1
+        }
+
+        do! ts |> TaskSeq.iter ignore
+        do! ts |> TaskSeq.iter ignore
+        do! ts |> TaskSeq.iter ignore
+        disposeCount.Value |> should equal 3
+    }
+
+    [<Fact>]
+    let ``CE taskSeq: use! - DisposeAsync called exactly once per full iteration`` () = task {
+        let disposeCount = ref 0
+
+        let ts = taskSeq {
+            use! _ = task { return new CountingAsyncDisposable(disposeCount) }
+            yield 1
+        }
+
+        do! ts |> TaskSeq.iter ignore
+        disposeCount.Value |> should equal 1
+    }
+
+    [<Fact>]
+    let ``CE taskSeq: use! - DisposeAsync called on each re-iteration`` () = task {
+        let disposeCount = ref 0
+
+        let ts = taskSeq {
+            use! _ = task { return new CountingAsyncDisposable(disposeCount) }
+            yield 1
+        }
+
+        do! ts |> TaskSeq.iter ignore
+        do! ts |> TaskSeq.iter ignore
+        do! ts |> TaskSeq.iter ignore
+        disposeCount.Value |> should equal 3
+    }
+
+    [<Fact>]
+    let ``CE taskSeq: use - Dispose called on early termination via take`` () = task {
+        let disposeCount = ref 0
+
+        let ts = taskSeq {
+            use _ = new CountingDisposable(disposeCount)
+            yield 1
+            yield 2
+            yield 3
+        }
+
+        // Only take 1 item — enumerator is disposed before the rest of the sequence runs
+        do! ts |> TaskSeq.take 1 |> TaskSeq.iter ignore
+        disposeCount.Value |> should equal 1
+    }
+
+    [<Fact>]
+    let ``CE taskSeq: use - multiple use bindings each get their own Dispose`` () = task {
+        let disposeCount = ref 0
+
+        let ts = taskSeq {
+            use _ = new CountingDisposable(disposeCount)
+            use _ = new CountingDisposable(disposeCount)
+            yield 1
+        }
+
+        do! ts |> TaskSeq.iter ignore
+        disposeCount.Value |> should equal 2
+    }
+
+    [<Fact>]
+    let ``CE taskSeq: use - each re-iteration creates and disposes a fresh resource`` () = task {
+        let createCount = ref 0
+
+        let ts = taskSeq {
+            createCount.Value <- createCount.Value + 1
+            use _ = new CountingDisposable(ref 0) // fresh ref each time
+            yield createCount.Value
+        }
+
+        let! first = ts |> TaskSeq.toListAsync
+        let! second = ts |> TaskSeq.toListAsync
+
+        // Each re-iteration re-runs the CE body and creates a new resource
+        first |> should equal [ 1 ]
+        second |> should equal [ 2 ]
+        createCount.Value |> should equal 2
+    }