Nowadays testing has become an integral part of every modern web application. Usually the term testing implies unit and functional testing. Unit testing is about testing our PHP classes. Every single PHP class is considered to be a unit, thus the name unit test. Functional tests on the other hand test various layers of our application, usually concentrated on testing the functionality overall, like the sign in or sign up process.

The PHP ecosystem has a great unit testing framework called PHPUnit, available for download at https://phpunit.de. It enables us to write primarily unit, but also functional type tests. The great thing about Symfony is that it comes with built in support for PHPUnit.

Before we can start running Symfony's tests, we need to make sure we have PHPUnit installed and available as console command. When executed, PHPUnit automatically tries to pick up and read testing configuration from phpunit.xml or phpunit.xml.dist within the current working directory, if available...