[Fact]
        public void TestWithObsoleteDisposeAsync()
        {
            string source = @"
class C : System.IAsyncDisposable
{
    public static async System.Threading.Tasks.Task Main()
    {
        using await (var x = new C())
        {
        }
    }
    [System.Obsolete]
    public async System.Threading.Tasks.ValueTask DisposeAsync()
    {
        await System.Threading.Tasks.Task.Delay(10);
    }
}
";
            var comp = CreateCompilationWithTasksExtensions(source + s_interfaces, options: TestOptions.DebugExe);
            comp.VerifyDiagnostics();
            // PROTOTYPE(async-streams) Confirm whether this behavior is ok (currently matching behavior of obsolete Dispose in non-async using)
        }