How can I assert the duration of the synchronous part of an async call?

Question

I need to assert that the initial synchronous part of an async method executes within a certain duration. Is this possible with fluent assertions? I also need to assert the minimum and maximum total duration (eg, using CompleteWithinAsync and NotCompleteWithinAsync), so the solution needs to cover all three timings (see my other question How do I assert that an async task should complete within a minimum and maximum time?) on a single task call/await expression.

Answer 1

The trivial and contrived, seems to function as expected.

using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using FluentAssertions;
                    
public class Program
{
    public static async Task Main()
    {
        // Arrange
        static async Task someAsyncBehaviourMock()
        {
            await Task.Yield();
            await Task.Delay(1000);
        };
        
        var s1 = Stopwatch.StartNew();
        var s2 = Stopwatch.StartNew();
        // Act
        var task = Target(someAsyncBehaviourMock);
        s1.Stop();
        await task;
        s2.Stop();
        
        // Assert
        s1.ElapsedMilliseconds.Should().BeGreaterThan(1000).And.BeLessThan(2000);
        s2.ElapsedMilliseconds.Should().BeGreaterThan(2000).And.BeLessThan(3000);
        
        Console.WriteLine(
            $"Success. s1:{s1.ElapsedMilliseconds}, s2:{s2.ElapsedMilliseconds}");
    }
    
    private static async Task Target(Func<Task> someAsyncBehaviour)
    {
        // Initial Sync Behaviour
        Thread.Sleep(1000);
        
        // Injected Async Behaviour
        await someAsyncBehaviour();
    }
}