def test_screen_name_minimum_length
  user = @valid_user
  min_length = User::SCREEN_NAME_MIN_LENGTH
    
  # Pseudonim jest zbyt krtki
  user.screen_name = "a" * (min_length - 1)
  assert !user.valid?, "#{user.screen_name} should raise a minimum length error"    
  # Formatuj komunikat o bdzie na podstawie minimalnej dugoci
  correct_error_message = sprintf(@error_messages[:too_short], min_length)
  assert_equal correct_error_message, user.errors.on(:screen_name)

  # Pseudonim ma minimaln dugo
  user.screen_name = "a" * min_length
  assert user.valid?, "#{user.screen_name} should be just long enough to pass"
end

