private void SetFactory(EssentialMode essentialMode)
        {
            switch (essentialMode)
            {
            case EssentialMode.Basic:
                learnerFactory = new BasicFactory();
                break;

            case EssentialMode.Advanced:
                learnerFactory = new AdvancedFactory();
                break;

            case EssentialMode.Async:
                learnerFactory = new AsyncFactory();
                break;
            }
        }
 public LearnerFactory(EssentialMode essentialMode) => SetFactory(essentialMode);