public async Task SomethingAsync_Throws_Exception()
 {
     var sut = new AsynchronousError();
     await Assert.ThrowsAsync <InvalidOperationException>(async() => {
         await sut.SomethingAsync();
     });
 }
        public void SomethingAsync_Return_Exception_AsyncContext()
        {
            var sut = new AsynchronousError();


            // using Nito.AsyncEx; is a help libary for async
            // it can help with testing async methods to avoid deadlocks a race conditions
            AsyncContext.Run(async() =>
            {
                await Assert.ThrowsAsync <InvalidOperationException>(async() => {
                    // Do not forget to await the task returned by ThrowAsync!
                    // If you forget to you test may pass silently a false positive
                    await sut.SomethingAsync();
                });
            });
        }