public void AddReaderTest()
{
Assert.AreEqual(0, _dataLayer.GetAllReaders().Count());
Reader person1 = new Reader(Guid.NewGuid(), "Adam", "Nowak", new DateTime(1998, 05, 23), "111222333", "*****@*****.**", Person.Gender.Male, new DateTime(2019, 9, 11));
_dataLayer.AddReader(person1);
Assert.AreEqual(1, _dataLayer.GetAllReaders().Count());
Assert.ThrowsException <ArgumentException>(() => _dataLayer.AddReader(person1));
}