public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ApplicationDbContext>(options =>
        options.UseInMemoryDatabase()
    );

    // Add framework services.
    services.AddMvc();

    // Register application services.
    services.AddScoped<ICharacterRepository, CharacterRepository>();
    services.AddTransient<IOperation, Operation>();
    services.AddSingleton<IJwtFactory, JWTFactory>();
    services.AddTransient<IOperationService, OperationService>();
}