From 47a9348a4b3e5ff2ef63d410f8cf883c27a64256 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Tue, 25 Aug 2026 18:02:28 +0000
Subject: [PATCH] Add test coverage for tryFirst, firstOrDefault,
 zipWithParallel, combineLatestWithAsync, toObservable

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 RELEASE_NOTES.md                              |  4 +
 .../AsyncSeqTests.fs                          | 91 +++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 47137e6..640ecba 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -1,3 +1,7 @@
+### Unreleased
+
+* Test coverage: Added tests for previously-untested public API functions `AsyncSeq.tryFirst`, `AsyncSeq.firstOrDefault`, `AsyncSeq.zipWithParallel`, `AsyncSeq.combineLatestWithAsync`, and `AsyncSeq.toObservable`. No functional changes.
+
 ### 4.17.0
 
 * Added `AsyncSeq.exists2` — asynchronously tests whether any corresponding pair of elements in two async sequences satisfies the predicate. Evaluates pairwise up to the shorter sequence; short-circuits on first match. Mirrors `Seq.exists2`.
diff --git a/tests/FSharp.Control.AsyncSeq.Tests/AsyncSeqTests.fs b/tests/FSharp.Control.AsyncSeq.Tests/AsyncSeqTests.fs
index 770f04c..c3738f3 100644
--- a/tests/FSharp.Control.AsyncSeq.Tests/AsyncSeqTests.fs
+++ b/tests/FSharp.Control.AsyncSeq.Tests/AsyncSeqTests.fs
@@ -5087,3 +5087,94 @@ let ``AsyncSeq.forall2Async returns true with async predicate`` () =
       (AsyncSeq.ofSeq [1;2;3])
     |> Async.RunSynchronously
   Assert.IsTrue(result)
+
+// ===== tryFirst / firstOrDefault =====
+
+[<Test>]
+let ``AsyncSeq.tryFirst returns Some first element for non-empty sequence`` () =
+  let result = AsyncSeq.tryFirst (AsyncSeq.ofSeq [1;2;3]) |> Async.RunSynchronously
+  Assert.AreEqual(Some 1, result)
+
+[<Test>]
+let ``AsyncSeq.tryFirst returns None for empty sequence`` () =
+  let result = AsyncSeq.tryFirst (AsyncSeq.empty<int>) |> Async.RunSynchronously
+  Assert.AreEqual(None, result)
+
+[<Test>]
+let ``AsyncSeq.firstOrDefault returns first element when non-empty`` () =
+  let result = AsyncSeq.firstOrDefault -1 (AsyncSeq.ofSeq [5;6;7]) |> Async.RunSynchronously
+  Assert.AreEqual(5, result)
+
+[<Test>]
+let ``AsyncSeq.firstOrDefault returns default when empty`` () =
+  let result = AsyncSeq.firstOrDefault -1 (AsyncSeq.empty<int>) |> Async.RunSynchronously
+  Assert.AreEqual(-1, result)
+
+// ===== zipWithParallel =====
+
+[<Test>]
+let ``AsyncSeq.zipWithParallel combines values from both sequences`` () =
+  let result =
+    AsyncSeq.zipWithParallel (fun a b -> a + b) (AsyncSeq.ofSeq [1;2;3]) (AsyncSeq.ofSeq [10;20;30])
+    |> AsyncSeq.toArrayAsync
+    |> Async.RunSynchronously
+  Assert.AreEqual([| 11;22;33 |], result)
+
+[<Test>]
+let ``AsyncSeq.zipWithParallel stops at shorter sequence`` () =
+  let result =
+    AsyncSeq.zipWithParallel (fun a b -> a, b) (AsyncSeq.ofSeq [1;2]) (AsyncSeq.ofSeq ["a";"b";"c"])
+    |> AsyncSeq.toArrayAsync
+    |> Async.RunSynchronously
+  Assert.AreEqual([| (1,"a"); (2,"b") |], result)
+
+// ===== combineLatestWithAsync =====
+
+[<Test>]
+let ``AsyncSeq.combineLatestWithAsync combines initial values then emits on each new update`` () =
+  let result =
+    AsyncSeq.combineLatestWithAsync
+      (fun a b -> async { return a + b })
+      (AsyncSeq.ofSeq [1;2])
+      (AsyncSeq.ofSeq [10])
+    |> AsyncSeq.toArrayAsync
+    |> Async.RunSynchronously
+  // First combination of initial pair, then subsequent updates to source1 combined with latest source2 value.
+  Assert.AreEqual([| 11; 12 |], result)
+
+[<Test>]
+let ``AsyncSeq.combineLatestWithAsync produces empty sequence when either source is empty`` () =
+  let result =
+    AsyncSeq.combineLatestWithAsync
+      (fun a b -> async { return a + b })
+      (AsyncSeq.empty<int>)
+      (AsyncSeq.ofSeq [1;2;3])
+    |> AsyncSeq.toArrayAsync
+    |> Async.RunSynchronously
+  Assert.AreEqual([||], result)
+
+// ===== toObservable =====
+
+type private TestObserver<'T>(onNext, onCompleted) =
+  interface IObserver<'T> with
+    member _.OnNext(v) = onNext v
+    member _.OnCompleted() = onCompleted ()
+    member _.OnError(_e) = ()
+
+[<Test>]
+let ``AsyncSeq.toObservable emits all values then completes`` () =
+  let received = ResizeArray<int>()
+  let completedEvent = new System.Threading.ManualResetEventSlim(false)
+  let observer = TestObserver<int>(received.Add, completedEvent.Set)
+  use _sub = (AsyncSeq.toObservable (AsyncSeq.ofSeq [1;2;3])).Subscribe(observer)
+  Assert.IsTrue(completedEvent.Wait(2000))
+  Assert.AreEqual([| 1;2;3 |], received.ToArray())
+
+[<Test>]
+let ``AsyncSeq.toObservable on empty sequence emits nothing`` () =
+  let received = ResizeArray<int>()
+  let completedEvent = new System.Threading.ManualResetEventSlim(false)
+  let observer = TestObserver<int>(received.Add, completedEvent.Set)
+  use _sub = (AsyncSeq.toObservable (AsyncSeq.empty<int>)).Subscribe(observer)
+  Assert.IsTrue(completedEvent.Wait(2000))
+  Assert.AreEqual([||], received.ToArray())