composer.json

{
    "require": {
        "symfony/console": "2.3.*"
    }
}

MyCommand.php

<?php

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputOption;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;

class MyCommand extends Command
{
    public function configure()
    {
        $this
            ->setName('acme:foo')
            ->setDescription('Foobar')
            ->addOption('bar', null, InputOption::VALUE_NONE);
    }

    public function execute(InputInterface $i, OutputInterface $o)
    {
        if ($i->getOption('bar')) {
            $o->writeln('BAR');
        } else {
            $o->writeln('FOO');
        }
    }
}

MyCommandTest.php

<?php

require_once __DIR__.'/vendor/autoload.php';
require_once __DIR__.'/MyCommand.php';

use Symfony\Component\Console\Application;
use Symfony\Component\Console\Tester\CommandTester;

class MyCommandTest extends \PHPUnit_Framework_TestCase
{
    public function testExecute()
    {
        $application = new Application();
        $application->add(new MyCommand());

        $command = $application->find('acme:foo');
        $commandTester = new CommandTester($command);
        $commandTester->execute(
            array(
                '--bar' => true,
//                'command' => 'acme:foo',
            )
        );

        $this->assertRegExp('{BAR}', $commandTester->getDisplay());
    }
}