Testing Concurrency's Implicit Cancellation

[tourultimate]

@Jon_Shier

• Double wrapping the Task s, thinking that I might need an owning Task to properly propagate the cancellation.

func testThatDataTaskIsCancelledInChildTask() async {
    // Given
    let session = stored(Session())
    let request = session.request(.get)

    // When
    let task = Task {
        _ = await Task {
            _ = await request.decode(TestResponse.self).response
        }.value
    }
    task.cancel()
    _ = await task.value

    // Then
    XCTAssertTrue(request.error?.isExplicitlyCancelledError == true)
    XCTAssertTrue(task.isCancelled, "Parent Task should be cancelled.")

The double-wrapped task is not a child, not implicitly cancelled in that case.

regarding this:

@Jon_Shier

• Cancelling a wrapping Task :

func testThatDataTaskIsCancelledInChildTask() async {
    // Given
    let session = stored(Session())
    let request = session.request(.get)

    // When
    let task = Task {
        _ = await request.decode(TestResponse.self).response
    }
    task.cancel()
    _ = await task.value

    // Then
    XCTAssertTrue(request.error?.isExplicitlyCancelledError == true)
    XCTAssertTrue(task.isCancelled, "Parent Task should be cancelled.")
}

In this case, task.isCancelled is still false, which doesn't make sense to me.

That is a bug. Try this instead:

func testThatDataTaskIsCancelledInChildTask() async {
    // Given
    let session = stored(Session())
    let request = session.request(.get)

    // When
    let task = Task {
        await Task.yield()
        // Task, not task
        XCTAssertTrue(Task.isCancelled, "Current Task should be cancelled.")
        _ = await request.decode(TestResponse.self).response
    }
    task.cancel()
    _ = await task.value

    // Then
    XCTAssertTrue(request.error?.isExplicitlyCancelledError == true)
}