Fixtures (Eng. fixtures) - a very useful development tool. Essentially, it is just a set of test data used in dev mode. They are typically not used in prod mode (for production, Data Migrations are usually used).
There are several convenient bundles for working with fixtures in Symfony. The first one is the basic DoctrineFixturesBundle, which is dedicated to this article.
This book became a kind of discovery for me. But first, a little bit of "poetry". =)
It just so happened that I love complex reading material. However, one should be very careful in this regard, as "complex reading material" can be at the level of Coelho (may all his fans forgive me, but it is difficult (for me) to find another bright example), or it can be something that truly changes you, for the better, towards less entropy (this was said under the impression of the book by Penrose). So what is the difference?