When async-await change thread?

Question

• When I call test1() method then ManagedThreadId will be changed after Delay(1).
• When I call test2() method (instead of test1()) then ManagedThreadId will stay

Answer 1

test1 awaits Task.Delay(1), which isn't going to be completed at the time it goes to await it, meaning the rest of test1 needs to be scheduled as a continuation.

For test2 you're awaiting Task.FromResult, which will always return an already completed Task. When you await an already completed task the method can just keep running on the current thread, without needing to schedule a continuation.