public void Add(Test test)
 {
     testRepository.AddTest(test);
 }
        static void Main(string[] args)
        {
            ITestRepository testRepository = new TestRepository();
            UserPrompts     userPrompts    = new UserPrompts(testRepository);

            Console.WriteLine("***Welcome to PBK 1.0 test platform!***\n");
            Console.WriteLine(@"In this application you can:

             *Take tests
             *Create tests
             *Change tests
             ");
            var userAnsw = true;

            do
            {
                Console.WriteLine("Please, enter the following number:\n" +
                                  "1)Take test\n" +
                                  "2)Create test\n" +
                                  "3)Change test\n" +
                                  "4)Show statistics\n ");

                int    userChoise;
                string Userline;
                bool   parsed;

                do
                {
                    /* || Возвращает true, если хотя бы один из операндов возвращает true. */
                    Userline = Console.ReadLine();
                    parsed   = int.TryParse(Userline, out userChoise);
                    if (string.IsNullOrWhiteSpace(Userline))
                    {
                        Console.WriteLine("!!!Alert!!!\n Empty input, please choose something");
                    }
                    else
                    {
                        if (!parsed)
                        {
                            Console.WriteLine($"!!!Alert!!!\n {Userline} is not a number, please, try again..");
                        }
                        else
                        {
                            if ((userChoise > 4 || userChoise < 1))
                            {
                                Console.WriteLine("Incorrect number, try a different");
                            }
                        }
                    }
                } while (!parsed || (userChoise > 4 || userChoise < 1));

                switch (userChoise)
                {
                case 1:

                    string testTopic = userPrompts.PromptForTargetRandomTestId();
                    var    test      = testRepository.GetRandomTestByTopic(testTopic);

                    TestService service = new TestService(test);
                    service.TakeTest();
                    break;

                case 2:
                    var newTest = Test.CreateTest();
                    testRepository.AddTest(newTest);


                    break;

                case 3:
                    var testId      = userPrompts.PromptsForUpdatingTestById();
                    var updatedTest = Test.UpdateTest(testId);
                    testRepository.UpdateTest(updatedTest);

                    break;

                case 4:
                    userPrompts.PromptForShowStatistics();

                    break;
                }
                Console.WriteLine("Exit from programm? y/n");
                var userEnter = Console.ReadLine();
                if (userEnter == "y")
                {
                    userAnsw = false;
                }
                else
                {
                    if (userEnter == "n")
                    {
                        userAnsw = true;
                    }
                    else
                    {
                        Console.WriteLine("Uncorrect enter");
                    }
                }
            } while (userAnsw != false);
        }