program.rb

class Person
  attr_accessor :first_name, :last_name, :birth_year, :car_registration

  def initialize(first_name, last_name, birth_year, car_registration)
    @first_name = PersonDataChecker.check_name(first_name)
    @last_name = PersonDataChecker.check_name(last_name)
    @birth_year = PersonDataChecker.check_birth_year(birth_year)
    @car_registration = PersonDataChecker.check_car_registration(car_registration)
  end
end

class PersonDataChecker
  def self.check_name(name)
    raise "Text field should not be empty" if name.empty?
    raise "Text should have 3 or more charachters" if name.length < 3
    raise "First letter must be uppercase" unless /[[:upper:]]/.match(name)
  end

  def self.check_birth_year(year)
    raise "Birth year must be between 1900 and 2020" unless (1900..2020).to_a.include?(year)
  end

  def self.check_car_registration(registration)
    canton_code = registration[0..1]
    number_code = registration[2..-1]

    raise "Registration number must contain two letters at the beginning" unless canton_code.match(/^[[:alpha:][:blank:]]+$/)
    raise "Registration number must containt at least 6 digits" if number_code.length > 6
  end
end

hans = Person.new("Hans", "Ruedi", 1987, "A333999")