public void IsInValidCityForBookTest()
{
BookValidator vld = new BookValidator();
string city = null;
Assert.AreEqual(false, vld.IsValidCity(city));
}
public void IsValidCityForBookTest()
{
BookValidator vld = new BookValidator();
string city = "Саратов";
Assert.AreEqual(true, vld.IsValidCity(city));
}