Are internal developments of companies tested separately from projects where they are used?

Question

Software testing

Welcome all. Take for example ClickHouse in Yandex.Metrica, Tarantool - in Mail.ru Mail. I wonder if these databases in the listed companies are tested only as part of project testing or are they checked separately? I’ll expand on the idea: is the task set to test Tarantool outside the services where it is used (there are testers allocated at least for a while who, on such an amount of anonymized test data, such a load, in such an emergency situation, watch how the database behaves) or only play user scenarios within the project (a team of project testers conducts load and automated testing when so many users are in Mail, sent letters with such and such content, etc.)
Do not give an analogy, if I have a project with PostgreSQL and ElasticSearch, then do I test them separately. No, of course, this is not invented here and tested on many similar projects around the world, most of the jambs surfaced by themselves in this way. On the other hand, there are vacancies for testers in Postgres Professional: the database itself is tested there, which means (?). I'm just wondering when a company has X development in-house (it doesn't matter if it's closed source or open source), and whether resources are planned to test it separately from all products. Thanks in advance

Answer 1

Tarantool is a separate product with a separate development cycle in general and testing in particular, it is not tested on any public Mail.Ru products.
As far as I can see, https://github.com/tarantool also has functional tests and benchmarks.

Answer 2

Short answer: Yes, it is being tested.
Long answer:
Teams developing these tools are always a relatively independent team, existing in their development cycles, releases, and their environment.
Testing of such a product can be tied to those "clients" who have integrated this product (i.e. during "internal testing"), use cases of external clients are taken into account. This is how testing of any product works - you, first of all, need to guarantee the work of those scenarios that are used by your users.
However, the product is likely to be tested in isolation from external integrations.