Shared VerifyFrameworkServicesTest helper

[HaoK]

So I think we can now have a shared test method which validates AddXyz setups ApplicationServices properly now that we can do this in a standard way for all of the AddFramework() methods...

cc @davidfowl @divega Thoughts?

public void VerifyAddFrameworkServices(Action<IServiceCollection> addServices, IEnumerable<Type> requiredServices>) {
    var context = new HostingContext();
    addServices(context.Services);
    var appServices = HostingEngine.CreateApplicationServices(context);
    foreach (var serviceType in requiredServices) {
        Assert.NotNull(appServices.GetRequiredService(serviceType));
    }    
}

[Fact]
void VerifyAddIdentity() {
    VerifyAddFrameworkServices(services => services.AddIdentity<TUser, TRole>(), 
          new Type[] { typeof(UserManager<TUser, TRole>), typeof(RoleManager<TRole>));
}

[Eilon]

@HaoK any interest in building this helper? Would it still be useful?

[HaoK]

Sure, I'm guessing most repos have some form of verifying this already, but could be useful to standardize

[Eilon]

I put it on your plate for beta7.

[HaoK]

Didn't get a chance to get to this for beta 7 it looks like. Backlog might be better than beta 8 at this point I'm guessing

[Eilon]

Alright with me.

[Eilon]

Ancient bug and doesn't look like we need/care anymore.