Awaiting an empty Task spins forever (await new Task(() => { }))

Question

I'm trying to get my head around this code:

 [TestFixture]
 public class ExampleTest
 {
    [Test]
    public void Example()
    {
        AwaitEmptyTask().Wait();
    }

    public async Task AwaitEmptyTask()
    {
        await new Task(() => { });
    }
 }

The method Example never ends and blocks forever. Why??

The fix (from Stubbing Task returning method in async unit test) is to replace await new Task( () => {}) with return Task.FromResult<object>(null); but again, why is this necessary?

I know there are a bunch of questions similar to this one, but none that I've seen seem to explain why this is happening:

• Await method that returns Task - spins forever?: I included the await keyword AFAIK correctly
• Stubbing Task returning method in async unit test: Doesn't explain why.
• Why will an empty .NET Task not complete if started and waited for from a static constructor?: I'm not running in a static context and as far as I can tell the context is consistent
• Async methods return null: also gives the solution, but doesn't explain why
• async await return Task: discusses Task.FromResult but not why await new Task(() => {}) doesn't work

Answer 1

You're creating a task and never starting it, so it never finishes.

You should be using Task.Run to create a task that you want to start executing immediately, rather than using the Task constructor.