provideRequirements() as $collection) {
            $output->writeln('');
            $output->writeln($collection->getName() . ' requirements : ');
            $output->writeln('');
            foreach ($collection->getRequirements() as $requirement) {
                $result = $requirement->isFulfilled() ? 'OK       ' : ($requirement->isOptional() ? 'WARNING  ' : 'ERROR    ');
                $output->write(' ' . $result);
                $output->writeln($requirement->getTestMessage());
                if (!$requirement->isFulfilled()) {
                    $ret = static::CHECK_ERROR;
                    $output->writeln("          " . $requirement->getHelpText());
                    $output->writeln('');
                }
            }
            $output->writeln('');
            $output->writeln($collection->getName() . ' recommendations : ');
            $output->writeln('');
            foreach ($collection->getRecommendations() as $requirement) {
                $result = $requirement->isFulfilled() ? 'OK       ' : ($requirement->isOptional() ? 'WARNING  ' : 'ERROR    ');
                $output->write(' ' . $result);
                $output->writeln($requirement->getTestMessage());
                if (!$requirement->isFulfilled()) {
                    if ($ret === static::CHECK_OK) {
                        $ret = static::CHECK_WARNING;
                    }
                    $output->writeln("          " . $requirement->getHelpText());
                    $output->writeln('');
                }
            }
        }
        return $ret;
    }
    /**
     * @return array An array of RequirementsCollection
     */
    abstract protected function provideRequirements();
}