Möchte man einen Integrationstest schreiben und dabei dependency injection nutzen, muss man folgendermaßen vorgehen:

1. Im Besten Fall teilt ma die Ausführende Applikation z.B. Web Applikation, Console etc und eine Bibliothek.
2. In die Bibliothek kommt die Auslagerung der StartUp:
   
   C#

   public static class ServiceCollectionExtensions { public static void UseMyModule(this IServiceCollection services) { services.AddTransient<IMyClass, MyClass>(); } }

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   public static class ServiceCollectionExtensions     {         public static void UseMyModule(this IServiceCollection services)         {             services.AddTransient<IMyClass, MyClass>();         }     }

3. Im Testprojekt wird eine Basis Klasse definiert, die dieses Modul einliest. Nun kann in CofigureServices services.UseMyModule() aufgerufen werden oder der Host selbst gebaut werden:
   
   C#

   [TestClass] public class BaseTestUnit { public static IHost Host { get; set; } [AssemblyInitialize] public static void ClassInitialize(TestContext context) { Host = AssemblyInit(context); } public static IHost AssemblyInit(TestContext context) { var host = Microsoft.Extensions.Hosting.Host.CreateDefaultBuilder(new string[0]) .ConfigureHostConfiguration(webHost => { }) .ConfigureAppConfiguration((hostContext, config) => { // AppSettings nach MachineName auslesen config .SetBasePath(System.IO.Directory.GetCurrentDirectory()) .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true) .AddJsonFile($"appsettings.{hostContext.HostingEnvironment.EnvironmentName}.json", optional: true) .AddJsonFile($"appsettings.{Environment.MachineName}.json", optional: true) .AddEnvironmentVariables(); }) .ConfigureServices((hostContext, services) => { services.AddOptions(); services.Configure<Application.Configuration.Configuration>(hostContext.Configuration.GetSection("Section in AppSettings")); NLog.Logger logger = NLog.LogManager.GetLogger("NLog Name"); services.AddSingleton(logger); services.Configure((Localization.Configuration.LocalizationConfiguration options) => hostContext.Configuration.GetSection("Localization Section in AppSettings").Bind(options)); services.AddSingleton<Localization.ILocalizationService, Localization.LocalizationService>(); services.AddSingleton<IMyClass, MyClass>(); }); return host.Start(); } public T GetService<T>() => (T)Host.Services.GetService(typeof(T)); }

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   [TestClass]     public class BaseTestUnit {           public static IHost Host { get; set; }                   [AssemblyInitialize]         public static void ClassInitialize(TestContext context) {             Host = AssemblyInit(context);                     }                   public static IHost AssemblyInit(TestContext context) {               var host = Microsoft.Extensions.Hosting.Host.CreateDefaultBuilder(new string[0])                 .ConfigureHostConfiguration(webHost =>                 {                   })                 .ConfigureAppConfiguration((hostContext, config) =>                 {                     // AppSettings nach MachineName auslesen                     config                         .SetBasePath(System.IO.Directory.GetCurrentDirectory())                         .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)                         .AddJsonFile($"appsettings.{hostContext.HostingEnvironment.EnvironmentName}.json", optional: true)                         .AddJsonFile($"appsettings.{Environment.MachineName}.json", optional: true)                         .AddEnvironmentVariables();                 })                 .ConfigureServices((hostContext, services) =>                 {                     services.AddOptions();                     services.Configure<Application.Configuration.Configuration>(hostContext.Configuration.GetSection("Section in AppSettings"));                                           NLog.Logger logger = NLog.LogManager.GetLogger("NLog Name");                     services.AddSingleton(logger);                       services.Configure((Localization.Configuration.LocalizationConfiguration options) => hostContext.Configuration.GetSection("Localization Section in AppSettings").Bind(options));                     services.AddSingleton<Localization.ILocalizationService, Localization.LocalizationService>();                       services.AddSingleton<IMyClass, MyClass>();                 });               return host.Start();         }           public T GetService<T>() => (T)Host.Services.GetService(typeof(T));       }

4. Die eigentliche Test Klasse erbt nun von diesen BaseUnitTest. Nun kann ein Propertiy erzeugt werden, welche einen Service aus der Dependency Injection ausliest:
   
   C#

   public MyClass MyClass => base.GetService<MyClass>();

   1	public MyClass MyClass => base.GetService<MyClass>();