public void ConfigureOptionsRegistersClassAsIValidatableIntoDiContainer()
{
IConfiguration cfg = new ConfigurationBuilder().Build();
var services = new ServiceCollection();
services.ConfigureOptions <ValidatableTestSettings>(cfg);
ServiceProvider provider = services.BuildServiceProvider();
IValidatable settings = provider.GetRequiredService <IValidatable>();
settings.Should().NotBeNull();
settings.Should().BeOfType <ValidatableTestSettings>();
}