Building software is a complex and sometimes tedious process in which you make errors and mistakes. Testing for errors is mostly done by running your website / code through tests either manually or automatically.
Checking for your code style like formatting and documentation flaws you can use a code sniffer. For PHP you can run
phpcs using PHP_CodeSniffer.
Drupal core provides
core/phpcs.xml.dist to tell phpcs what to test for.