Program.cs

public class Program
    {
        public static void Main(string[] args)
        {
            CreateWebHostBuilder(args).Run();
        }

        public static IWebHost CreateWebHostBuilder(string[] args)
        {
            var hostBuilder = WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>();

            var host = hostBuilder.Build();

            using (var scope = host.Services.CreateScope())
            {
                var dbContext = scope.ServiceProvider.GetService<ApplicationDbContext>();

                dbContext.Database.EnsureCreated();

                dbContext.Add(new IdentityRole
                {
                    Name = "Test",
                    NormalizedName = "TEST"
                });
                dbContext.SaveChanges();
            }

            return host;
        }
            
    }