Assuming you use sqlite in prod or are willing to take the L if some minor db difference breaks prod...

This method is actually super popular in the PHP world, but people get themselves into trouble if they tidy up all the footguns that stock sqlite leaves behind for you (strict types being a big one).

Also, when you get a certain size of database, certain operations can become hideously slow (and that can change depending on the engine as well) but if you're running a totally different database for your test suite, it's one more thing that is different.

I do recognize that these are niche problems for healthy companies that can afford to solve them, so ymmv.