def test_screen_name_length_boundaries
  assert_length :min, @valid_user, :screen_name, User::SCREEN_NAME_MIN_LENGTH
  assert_length :max, @valid_user, :screen_name, User::SCREEN_NAME_MAX_LENGTH
end
  
def test_password_length_boundaries
  assert_length :min, @valid_user, :password, User::PASSWORD_MIN_LENGTH
  assert_length :max, @valid_user, :password, User::PASSWORD_MAX_LENGTH
end

