public static TImplementation AssertRegisteredSingleton <TInterface, TImplementation>(this IServiceProvider provider)
 => (TImplementation)provider.AssertRegisteredSingleton(typeof(TInterface), typeof(TImplementation));
 public void ShouldRegisterSingletonTypes(Type interfaceType, Type implementationType)
 {
     _provider.AssertRegisteredSingleton(interfaceType, implementationType);
 }