One of the most common runtime exceptions or errors I face using Dot Net Core is that a service is not registered for Dependency Injection. This post focuses on the Microsoft.Extensions.DependencyInjection library. Registering dependencies is a required step anytime a new service created and I often forget. I have found a way to easily test and ensure services are generated properly from the service provider (also known as the dependency injection container).
Below is a sample extension method used by a class library to register its services in the Applications container. This is fairly common practice with class libraries. I often forget to add to these as the number of services increase.
namespace MyApp.Services
{
public static class RegisterServices
{
public static IServiceCollection UseTextServices(this IServiceCollection services)
{
services.AddScoped<ITextService,TextService>();
return services;
}
}
}Let’s take a look at a way to test and ensure we generate our service from the provider without error. The method below builds a ServiceProvider object using our extension method. After the service provider is built, we can use the GetService<T>() to retrieve our service and ensure it returns the correct type. When using the GetService<T>() method, you want to use the interface like you would when implementing through a constructor.
namespace MyApp.Test
{
public class RegisterServicesTest
{
[Fact]
public void TestServiceRegistration()
{
ServiceProvider provider = new ServiceCollection()
.UseTextServices()
.BuildServiceProvider();
Assert.IsType<TextService>(provider.GetService<ITextService>());
}
}
}This not only tests that services are registered, but anything those services depend on and so on. I would recommend adding unit tests to ensure your dependency injection provider is setup properly.