private static List <ServiceDescriptor> ConfigureServices()
{
var descriptors = new List <ServiceDescriptor>();
var services = Substitute.For <IServiceCollection>();
services.When(s => s.Add(Arg.Any <ServiceDescriptor>()))
.Do(args => descriptors.Add(args[0] as ServiceDescriptor));
var logger = Substitute.For <ILogger>();
var configure = new Singletons();
configure.Logger = logger;
configure.ConfigureServices(services);
return(descriptors);
}