How to test all ASP.NET Core Controllers Dependency Injection is valid?

Question

We occasionally have issues whereby someone adds some DI into a controller but forgets to add the relevant line into Startup.cs to set the scope of the object.

This does not prevent the application from starting, but rather, throws an exception when the relevent endpoint is hit.

Is there any way of programmatically checking all controllers are valid and preventing the application from starting otherwise?

Alternatively is there an easy way to write a catch-all automated test to check every controller can be instantiated using the specified DI in Startup.cs?

Answer 1

Summarised from https://andrewlock.net/new-in-asp-net-core-3-service-provider-validation/, please see link for more details.

As of ASP.NET 3.0 there is now a way to validate controller dependencies on build:

Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers()
        .AddControllersAsServices(); // This part adds Controllers to DI

Program.cs:

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            })
            .UseDefaultServiceProvider((context, options) =>
            {
                options.ValidateScopes = context.HostingEnvironment.IsDevelopment();
                // Validate DI on build
                options.ValidateOnBuild = true;
            });

Notes:

• Service provider validation is only enabled in the Development environment by default.
• Will not work for run-time ServiceProvider look ups (service locator pattern) e.g. _service = provider.GetRequiredService<MyService>();
• Will not work for [FromServices] parameters in methods (i.e. it only checks constructor dependencies)
• Will not work for 'open generics' e.g. services.AddSingleton(typeof(MyServiceWithGeneric<>));
• Will not work for services registered with factory functions e.g.

    services.AddSingleton<MyService>(provider => 
    {
        var nestedService = provider.GetRequiredService<MyNestedService>();
        return new MyService(nestedService);
    });