public void RemoveBookExampleTest()
{
TestRepository testRepository = new TestRepository();
DataService dataService = new DataService(testRepository);
Book book = new Book("Pan Tadeusz1", "Adam M", Guid.Parse("52D2DA0E-22C1-4A0E-BF60-96859EB5A143"));
BookExample bookExample = new BookExample(book, 23, 60);
testRepository.AddBookExample(bookExample);
dataService.RemoveBookExample(bookExample);
Assert.AreEqual(0, testRepository.bookExamples.Count);
}