gist.php

<?php
protected function interact(InputInterface $input, OutputInterface $output)
{
    $dialog    = $this->getDialogHelper();
    $validator = Validation::createValidator();

    $inputValue = $dialog->ask($output, 'Enter some input: ');
    $errors = $validator->validateValue($inputValue, new Assert\NotBlank());
    if (count($errors)) {
        throw new \RuntimeException('Input cannot be blank');
    }
}