Custom WebApplicationFactory in integration testing not registering services in Startup.cs (ASP.NET Core 3.1)

I am running into an issue where I am using a custom WebApplicationFactory and it is not registering the services in my Startup.cs. I am using Asp.Net core 3.1 and Xunit.

I have below in my API (startup.cs) registered using extension methods:

public void ConfigureServices(IServiceCollection services)
        {
            services.AddBaseApiConfiguration(Configuration);

            services.AddRepositoryServices();

            services.AddApiServices();

            services.AddMediatrServices();
        }

Per MS documentation:

The SUT's database context is registered in its Startup.ConfigureServices method. The test app's builder.ConfigureServices callback is executed after the app's Startup.ConfigureServices code is executed.

But above is not occurring. None of my services from the startup I am using are being registered (i.e. the 4 extension methods I have are never being called and are never registered). This is causing a few problems: my DB context uses IMediatr in its constructor so that events can be published during context.SaveChangesAsync() (on success). But as my service is never registered, it fails to find it. How do I ensure that this takes place correctly?

Below is my custom factory:

    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder
        .UseEnvironment("Development")
        .ConfigureServices(services =>
        {
            // Remove the app's db context registrations
            var descriptor = services.SingleOrDefault(
                d => d.ServiceType ==
                    typeof(DbContextOptions<AppDbContext>));


            if (descriptor != null)
            {
                services.Remove(descriptor );
            }

            services.AddSingleton<IDbConnectionFactoryService, SqliteConnectionFactoryService>();

            // Add a database context using an in-memory 
            // database for testing.
            services.AddDbContext<AppDbContext>(options =>
            {
                options.UseSqlite("Data Source=sqlitedemo.db");
            });

            // Build the service provider.
            var sp = services.BuildServiceProvider();

            // Create a scope to obtain a reference to the database context 
            using (var scope = sp.CreateScope())
            {
                var scopedServices = scope.ServiceProvider;
                var db = scopedServices.GetRequiredService<AppDbContext>();

                // Ensure the database is created.
                db .Database.EnsureDeleted();
                db .Database.EnsureCreated();
            }
        });
    }

Edit: It seems the services in Startup.cs are being called after the CustomWebApplication factory services. This is completely odd as per .Net core 3.0, the order was changed to be the opposite. So why is this still occuring?

Edit 2: Need to use ConfigureTestServices instead of ConfigureServices.