Add CancellableQueueTests for 100% test coverage

Test cancelTasks() behavior across all queue types:
- FIFOQueue (with isolated and throwing variants)
- ActorQueue
- MainActor queue

Each queue type tests four scenarios:
- doesNotCancelCompletedTask
- cancelsCurrentlyExecutingTask
- cancelsCurrentlyExecutingAndPendingTasks
- doesNotCancelFutureTasks

Author: claude

Tests/AsyncQueueTests/CancellableQueueTests.swift

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+// MIT License
+//
+// Copyright (c) 2025 Dan Federman
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+import Foundation
+import Testing
+
+@testable import AsyncQueue
+
+struct CancellableQueueTests {
+	// MARK: FIFOQueue Tests
+
+	@Test
+	func cancelTasks_fifoQueue_doesNotCancelCompletedTask() async throws {
+		let systemUnderTest = CancellableQueue(underlyingQueue: FIFOQueue())
+		let expectation = Expectation()
+
+		// Create a task that completes immediately
+		let task = Task(on: systemUnderTest) {
+			expectation.fulfill()
+			try doWork()
+		}
+
+		// Wait for the task to complete
+		try await task.value
+
+		// Now cancel tasks - should have no effect since task already completed
+		systemUnderTest.cancelTasks()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_fifoQueue_cancelsCurrentlyExecutingTask() async {
+		let systemUnderTest = CancellableQueue(underlyingQueue: FIFOQueue())
+		let semaphore = Semaphore()
+		let expectation = Expectation()
+
+		// Create a task that waits on a semaphore
+		Task(on: systemUnderTest) {
+			await semaphore.wait()
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Give the task time to start executing and reach the semaphore
+		try? await Task.sleep(nanoseconds: 10_000_000)
+
+		// Cancel all tasks
+		systemUnderTest.cancelTasks()
+
+		// Signal the semaphore to let the task continue
+		await semaphore.signal()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_fifoQueue_cancelsCurrentlyExecutingAndPendingTasks() async {
+		let systemUnderTest = CancellableQueue(underlyingQueue: FIFOQueue())
+		let semaphore = Semaphore()
+		let counter = Counter()
+		let expectation = Expectation(expectedCount: 3)
+
+		// Create a task that waits on a semaphore (will be executing)
+		Task(on: systemUnderTest, isolatedTo: counter) { _ in
+			await semaphore.wait()
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Create pending tasks that won't start until the first task completes
+		Task(on: systemUnderTest, isolatedTo: counter) { _ in
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		Task(on: systemUnderTest, isolatedTo: counter) { _ in
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Give the first task time to start executing
+		try? await Task.sleep(nanoseconds: 10_000_000)
+
+		// Cancel all tasks
+		systemUnderTest.cancelTasks()
+
+		// Signal the semaphore to let tasks continue
+		await semaphore.signal()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_fifoQueue_doesNotCancelFutureTasks() async throws {
+		let systemUnderTest = CancellableQueue(underlyingQueue: FIFOQueue())
+		let counter = Counter()
+		let expectation = Expectation()
+
+		// Cancel tasks before creating any
+		systemUnderTest.cancelTasks()
+
+		// Create a task after cancellation - it should NOT be cancelled
+		let task = Task(on: systemUnderTest, isolatedTo: counter) { _ in
+			#expect(!Task.isCancelled)
+			expectation.fulfill()
+			try doWork()
+		}
+
+		try await task.value
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	// MARK: ActorQueue Tests
+
+	@Test
+	func cancelTasks_actorQueue_doesNotCancelCompletedTask() async throws {
+		let actorQueue = ActorQueue<Counter>()
+		let counter = Counter()
+		actorQueue.adoptExecutionContext(of: counter)
+		let systemUnderTest = CancellableQueue(underlyingQueue: actorQueue)
+		let expectation = Expectation()
+
+		// Create a task that completes immediately
+		let task = Task(on: systemUnderTest) { _ in
+			expectation.fulfill()
+			try doWork()
+		}
+
+		// Wait for the task to complete
+		try await task.value
+
+		// Now cancel tasks - should have no effect since task already completed
+		systemUnderTest.cancelTasks()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_actorQueue_cancelsCurrentlyExecutingTask() async {
+		let actorQueue = ActorQueue<Counter>()
+		let counter = Counter()
+		actorQueue.adoptExecutionContext(of: counter)
+		let systemUnderTest = CancellableQueue(underlyingQueue: actorQueue)
+		let semaphore = Semaphore()
+		let expectation = Expectation()
+
+		// Create a task that waits on a semaphore
+		Task(on: systemUnderTest) { _ in
+			await semaphore.wait()
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Give the task time to start executing and reach the semaphore
+		try? await Task.sleep(nanoseconds: 10_000_000)
+
+		// Cancel all tasks
+		systemUnderTest.cancelTasks()
+
+		// Signal the semaphore to let the task continue
+		await semaphore.signal()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_actorQueue_cancelsCurrentlyExecutingAndPendingTasks() async {
+		let actorQueue = ActorQueue<Counter>()
+		let counter = Counter()
+		actorQueue.adoptExecutionContext(of: counter)
+		let systemUnderTest = CancellableQueue(underlyingQueue: actorQueue)
+		let semaphore = Semaphore()
+		let expectation = Expectation(expectedCount: 3)
+
+		// Create a task that waits on a semaphore (will be executing)
+		Task(on: systemUnderTest) { _ in
+			await semaphore.wait()
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Create pending tasks that won't start until the first task suspends
+		Task(on: systemUnderTest) { _ in
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		Task(on: systemUnderTest) { _ in
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Give the first task time to start executing
+		try? await Task.sleep(nanoseconds: 10_000_000)
+
+		// Cancel all tasks
+		systemUnderTest.cancelTasks()
+
+		// Signal the semaphore to let tasks continue
+		await semaphore.signal()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_actorQueue_doesNotCancelFutureTasks() async throws {
+		let actorQueue = ActorQueue<Counter>()
+		let counter = Counter()
+		actorQueue.adoptExecutionContext(of: counter)
+		let systemUnderTest = CancellableQueue(underlyingQueue: actorQueue)
+		let expectation = Expectation()
+
+		// Cancel tasks before creating any
+		systemUnderTest.cancelTasks()
+
+		// Create a task after cancellation - it should NOT be cancelled
+		let task = Task(on: systemUnderTest) { _ in
+			#expect(!Task.isCancelled)
+			expectation.fulfill()
+			try doWork()
+		}
+
+		try await task.value
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	// MARK: MainActor Queue Tests
+
+	@Test
+	func cancelTasks_mainActorQueue_doesNotCancelCompletedTask() async throws {
+		let systemUnderTest = CancellableQueue(underlyingQueue: MainActor.queue)
+		let expectation = Expectation()
+
+		// Create a task that completes immediately
+		let task = Task(on: systemUnderTest) {
+			expectation.fulfill()
+			try doWork()
+		}
+
+		// Wait for the task to complete
+		try await task.value
+
+		// Now cancel tasks - should have no effect since task already completed
+		systemUnderTest.cancelTasks()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_mainActorQueue_cancelsCurrentlyExecutingTask() async {
+		let systemUnderTest = CancellableQueue(underlyingQueue: MainActor.queue)
+		let semaphore = Semaphore()
+		let expectation = Expectation()
+
+		// Create a task that waits on a semaphore
+		Task(on: systemUnderTest) {
+			await semaphore.wait()
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Give the task time to start executing and reach the semaphore
+		try? await Task.sleep(nanoseconds: 10_000_000)
+
+		// Cancel all tasks
+		systemUnderTest.cancelTasks()
+
+		// Signal the semaphore to let the task continue
+		await semaphore.signal()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_mainActorQueue_cancelsCurrentlyExecutingAndPendingTasks() async {
+		let systemUnderTest = CancellableQueue(underlyingQueue: MainActor.queue)
+		let semaphore = Semaphore()
+		let expectation = Expectation(expectedCount: 3)
+
+		// Create a task that waits on a semaphore (will be executing)
+		Task(on: systemUnderTest) {
+			await semaphore.wait()
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Create pending tasks that won't start until the first task suspends
+		Task(on: systemUnderTest) {
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		Task(on: systemUnderTest) {
+			#expect(Task.isCancelled)
+			expectation.fulfill()
+		}
+
+		// Give the first task time to start executing
+		try? await Task.sleep(nanoseconds: 10_000_000)
+
+		// Cancel all tasks
+		systemUnderTest.cancelTasks()
+
+		// Signal the semaphore to let tasks continue
+		await semaphore.signal()
+
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	@Test
+	func cancelTasks_mainActorQueue_doesNotCancelFutureTasks() async throws {
+		let systemUnderTest = CancellableQueue(underlyingQueue: MainActor.queue)
+		let expectation = Expectation()
+
+		// Cancel tasks before creating any
+		systemUnderTest.cancelTasks()
+
+		// Create a task after cancellation - it should NOT be cancelled
+		let task = Task(on: systemUnderTest) {
+			#expect(!Task.isCancelled)
+			expectation.fulfill()
+			try doWork()
+		}
+
+		try await task.value
+		await expectation.fulfillment(withinSeconds: 30)
+	}
+
+	// MARK: Private
+
+	@Sendable
+	private func doWork() throws {}
+}