Daily Test Coverage Improver: Add 13 comprehensive edge case and branch coverage tests

tests/FSharp.Control.AsyncSeq.Tests/AsyncSeqTests.fs

@@ -2113,3 +2113,114 @@ let ``Seq.ofAsyncSeq with exception should propagate``() =
 
 #endif
 
+// ----------------------------------------------------------------------------
+// Additional Coverage Tests targeting uncovered edge cases and branches
+
+[<Test>]
+let ``AsyncSeq.bufferByCount with size 1 should work`` () =
+  let source = asyncSeq { yield 1; yield 2; yield 3 }
+  let result = AsyncSeq.bufferByCount 1 source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([[|1|]; [|2|]; [|3|]], result)
+
+[<Test>]
+let ``AsyncSeq.bufferByCount with empty sequence should return empty`` () =
+  let result = AsyncSeq.bufferByCount 2 AsyncSeq.empty |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([], result)
+
+[<Test>]
+let ``AsyncSeq.bufferByCount with size larger than sequence should return partial`` () =
+  let source = asyncSeq { yield 1; yield 2 }
+  let result = AsyncSeq.bufferByCount 5 source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([[|1; 2|]], result)
+
+[<Test>]
+let ``AsyncSeq.pairwise with empty sequence should return empty`` () =
+  let result = AsyncSeq.pairwise AsyncSeq.empty |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([], result)
+
+[<Test>]
+let ``AsyncSeq.pairwise with single element should return empty`` () =
+  let source = asyncSeq { yield 42 }
+  let result = AsyncSeq.pairwise source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([], result)
+
+[<Test>]
+let ``AsyncSeq.pairwise with three elements should produce two pairs`` () =
+  let source = asyncSeq { yield 1; yield 2; yield 3 }
+  let result = AsyncSeq.pairwise source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([(1, 2); (2, 3)], result)
+
+[<Test>]
+let ``AsyncSeq.distinctUntilChangedWith should work with custom equality`` () =
+  let source = asyncSeq { yield "a"; yield "A"; yield "B"; yield "b"; yield "c" }
+  let customEq (x: string) (y: string) = x.ToLower() = y.ToLower()
+  let result = AsyncSeq.distinctUntilChangedWith customEq source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual(["a"; "B"; "c"], result)
+
+[<Test>]
+let ``AsyncSeq.distinctUntilChangedWith with all same elements should return single`` () =
+  let source = asyncSeq { yield 1; yield 1; yield 1 }
+  let result = AsyncSeq.distinctUntilChangedWith (=) source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([1], result)
+
+[<Test>]
+let ``AsyncSeq.append with both sequences having exceptions should propagate first`` () =
+  async {
+    let seq1 = asyncSeq { yield 1; failwith "error1" }
+    let seq2 = asyncSeq { yield 2; failwith "error2" }
+    let combined = AsyncSeq.append seq1 seq2
+
+    try
+      let! _ = AsyncSeq.toListAsync combined
+      Assert.Fail("Expected exception to be thrown")
+    with
+    | ex when ex.Message = "error1" -> 
+      () // Expected - first sequence's error should be thrown
+    | ex -> 
+      Assert.Fail($"Unexpected exception: {ex.Message}")
+  } |> Async.RunSynchronously
+
+[<Test>]
+let ``AsyncSeq.concat with nested exceptions should propagate properly`` () =
+  async {
+    let nested = asyncSeq {
+      yield asyncSeq { yield 1; yield 2 }
+      yield asyncSeq { failwith "nested error" }
+      yield asyncSeq { yield 3 }
+    }
+    let flattened = AsyncSeq.concat nested
+
+    try
+      let! result = AsyncSeq.toListAsync flattened
+      Assert.Fail("Expected exception to be thrown")
+    with
+    | ex when ex.Message = "nested error" -> 
+      () // Expected
+    | ex -> 
+      Assert.Fail($"Unexpected exception: {ex.Message}")
+  } |> Async.RunSynchronously
+
+[<Test>]
+let ``AsyncSeq.choose with all None should return empty`` () =
+  let source = asyncSeq { yield 1; yield 2; yield 3 }
+  let result = AsyncSeq.choose (fun _ -> None) source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([], result)
+
+[<Test>]
+let ``AsyncSeq.choose with mixed Some and None should filter correctly`` () =
+  let source = asyncSeq { yield 1; yield 2; yield 3; yield 4 }
+  let chooser x = if x % 2 = 0 then Some (x * 2) else None
+  let result = AsyncSeq.choose chooser source |> AsyncSeq.toListSynchronously
+  Assert.AreEqual([4; 8], result)
+
+[<Test>]
+let ``AsyncSeq.chooseAsync with async transformation should work`` () =
+  async {
+    let source = asyncSeq { yield 1; yield 2; yield 3; yield 4 }
+    let chooserAsync x = async {
+      if x % 2 = 0 then return Some (x * 3) else return None
+    }
+    let! result = AsyncSeq.chooseAsync chooserAsync source |> AsyncSeq.toListAsync
+    Assert.AreEqual([6; 12], result)
+  } |> Async.RunSynchronously
+