chore: import upstream snapshot with attribution

Tests/ContainerizationExtrasTests/AsyncLockTests.swift

@@ -0,0 +1,112 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2026 Apple Inc. and the Containerization project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import Testing
+
+@testable import ContainerizationExtras
+
+private final class Unprotected: @unchecked Sendable {
+    var value: Int
+    init(_ value: Int) { self.value = value }
+}
+
+final class AsyncLockTests {
+    @Test
+    func testBasicModification() async throws {
+        let lock = AsyncLock()
+        let counter = Unprotected(0)
+
+        let result = await lock.withLock { _ in
+            counter.value += 1
+            return counter.value
+        }
+
+        #expect(result == 1)
+    }
+
+    @Test
+    func testSequentialReturnValues() async throws {
+        let lock = AsyncLock()
+
+        let first = await lock.withLock { _ in 1 }
+        let second = await lock.withLock { _ in first + 1 }
+        let third = await lock.withLock { _ in second + 1 }
+
+        #expect(third == 3)
+    }
+
+    @Test
+    func testMultipleModifications() async throws {
+        let lock = AsyncLock()
+        let counter = Unprotected(0)
+
+        await lock.withLock { _ in
+            counter.value += 5
+        }
+
+        let result = await lock.withLock { value in
+            counter.value += 10
+            return counter.value
+        }
+
+        #expect(result == 15)
+    }
+
+    @Test
+    func testMutualExclusion() async throws {
+        let lock = AsyncLock()
+        let counter = Unprotected(0)
+        let iterations = 100
+
+        await withTaskGroup(of: Void.self) { group in
+            for _ in 0..<iterations {
+                group.addTask {
+                    await lock.withLock { _ in
+                        let current = counter.value
+                        try? await Task.sleep(for: .milliseconds(10))
+                        counter.value = current + 1
+                    }
+                }
+            }
+        }
+
+        #expect(counter.value == iterations)
+    }
+
+    @Test
+    func testThrowingClosure() async throws {
+        let lock = AsyncLock()
+        let counter = Unprotected(0)
+
+        await #expect(throws: POSIXError.self) {
+            try await lock.withLock { _ in
+                counter.value = 1
+                throw POSIXError(.ENOENT)
+            }
+        }
+
+        // Value should still be modified even though closure threw
+        #expect(counter.value == 1)
+
+        // Lock should still be usable even though the previous closure threw
+        await lock.withLock { _ in
+            counter.value = 2
+        }
+
+        #expect(counter.value == 2)
+    }
+}