public void ConfigureTest()
{
var startup = new ConfigureTestStartup2();
var hostBuilder = new HostBuilder().ConfigureServices(s => s.AddSingleton(startup));
var services = hostBuilder.Build().Services;
StartupLoader.Configure(services, new EmptyStartup());
Assert.Throws <InvalidOperationException>(() => StartupLoader.Configure(services, new ConfigureTestStartup0()));
Assert.Throws <InvalidOperationException>(() => StartupLoader.Configure(services, new ConfigureTestStartup1()));
StartupLoader.Configure(services, startup);
Assert.True(startup.Invoked);
}