[test] add a unit test for the LambdaHTTPServer Pool

Package@swift-6.0.swift

@@ -56,6 +56,11 @@ let package = Package(
                 .byName(name: "AWSLambdaRuntime"),
                 .product(name: "NIOTestUtils", package: "swift-nio"),
                 .product(name: "NIOFoundationCompat", package: "swift-nio"),
+            ],
+            swiftSettings: [
+                .define("FoundationJSONSupport"),
+                .define("ServiceLifecycleSupport"),
+                .define("LocalServerSupport"),
             ]
         ),
         // for perf testing

Sources/AWSLambdaRuntime/Lambda+LocalServer.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the SwiftAWSLambdaRuntime open source project
 //
-// Copyright (c) 2020 Apple Inc. and the SwiftAWSLambdaRuntime project authors
+// Copyright (c) 2025 Apple Inc. and the SwiftAWSLambdaRuntime project authors
 // Licensed under Apache License v2.0
 //
 // See LICENSE.txt for license information
@@ -75,7 +75,7 @@ extension Lambda {
 /// 1. POST /invoke - the client posts the event to the lambda function
 ///
 /// This server passes the data received from /invoke POST request to the lambda function (GET /next) and then forwards the response back to the client.
-private struct LambdaHTTPServer {
+internal struct LambdaHTTPServer {
     private let invocationEndpoint: String
 
     private let invocationPool = Pool<LocalServerInvocation>()
@@ -425,7 +425,7 @@ private struct LambdaHTTPServer {
     /// A shared data structure to store the current invocation or response requests and the continuation objects.
     /// This data structure is shared between instances of the HTTPHandler
     /// (one instance to serve requests from the Lambda function and one instance to serve requests from the client invoking the lambda function).
-    private final class Pool<T>: AsyncSequence, AsyncIteratorProtocol, Sendable where T: Sendable {
+    internal final class Pool<T>: AsyncSequence, AsyncIteratorProtocol, Sendable where T: Sendable {
         typealias Element = T
 
         enum State: ~Copyable {

Tests/AWSLambdaRuntimeTests/PoolTests.swift

@@ -0,0 +1,150 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftAWSLambdaRuntime open source project
+//
+// Copyright (c) 2025 Apple Inc. and the SwiftAWSLambdaRuntime project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftAWSLambdaRuntime project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Testing
+
+@testable import AWSLambdaRuntime
+
+struct PoolTests {
+
+    @Test
+    func testBasicPushAndIteration() async throws {
+        let pool = LambdaHTTPServer.Pool<String>()
+
+        // Push values
+        await pool.push("first")
+        await pool.push("second")
+
+        // Iterate and verify order
+        var values = [String]()
+        for try await value in pool {
+            values.append(value)
+            if values.count == 2 { break }
+        }
+
+        #expect(values == ["first", "second"])
+    }
+
+    @Test
+    func testCancellation() async throws {
+        let pool = LambdaHTTPServer.Pool<String>()
+
+        // Create a task that will be cancelled
+        let task = Task {
+            for try await _ in pool {
+                Issue.record("Should not receive any values after cancellation")
+            }
+        }
+
+        // Cancel the task immediately
+        task.cancel()
+
+        // This should complete without receiving any values
+        try await task.value
+    }
+
+    @Test
+    func testConcurrentPushAndIteration() async throws {
+        let pool = LambdaHTTPServer.Pool<Int>()
+        let iterations = 1000
+        var receivedValues = Set<Int>()
+
+        // Start consumer task first
+        let consumer = Task {
+            var count = 0
+            for try await value in pool {
+                receivedValues.insert(value)
+                count += 1
+                if count >= iterations { break }
+            }
+        }
+
+        // Create multiple producer tasks
+        try await withThrowingTaskGroup(of: Void.self) { group in
+            for i in 0..<iterations {
+                group.addTask {
+                    await pool.push(i)
+                }
+            }
+            try await group.waitForAll()
+        }
+
+        // Wait for consumer to complete
+        try await consumer.value
+
+        // Verify all values were received exactly once
+        #expect(receivedValues.count == iterations)
+        #expect(Set(0..<iterations) == receivedValues)
+    }
+
+    @Test
+    func testPushToWaitingConsumer() async throws {
+        let pool = LambdaHTTPServer.Pool<String>()
+        let expectedValue = "test value"
+
+        // Start a consumer that will wait for a value
+        let consumer = Task {
+            for try await value in pool {
+                #expect(value == expectedValue)
+                break
+            }
+        }
+
+        // Give consumer time to start waiting
+        try await Task.sleep(nanoseconds: 100_000_000)  // 0.1 seconds
+
+        // Push a value
+        await pool.push(expectedValue)
+
+        // Wait for consumer to complete
+        try await consumer.value
+    }
+
+    @Test
+    func testStressTest() async throws {
+        let pool = LambdaHTTPServer.Pool<Int>()
+        let producerCount = 10
+        let messagesPerProducer = 1000
+        var receivedValues = [Int]()
+
+        // Start consumer
+        let consumer = Task {
+            var count = 0
+            for try await value in pool {
+                receivedValues.append(value)
+                count += 1
+                if count >= producerCount * messagesPerProducer { break }
+            }
+        }
+
+        // Create multiple producers
+        try await withThrowingTaskGroup(of: Void.self) { group in
+            for p in 0..<producerCount {
+                group.addTask {
+                    for i in 0..<messagesPerProducer {
+                        await pool.push(p * messagesPerProducer + i)
+                    }
+                }
+            }
+            try await group.waitForAll()
+        }
+
+        // Wait for consumer to complete
+        try await consumer.value
+
+        // Verify we received all values
+        #expect(receivedValues.count == producerCount * messagesPerProducer)
+        #expect(Set(receivedValues).count == producerCount * messagesPerProducer)
+    }
+}