That makes testing faster, sure, but then when you deploy your app to production you can get lots of weird errors because SQLite is weakly typed and Postgres is

That makes testing faster, sure, but then when you deploy your app to production you can get lots of weird errors because SQLite is weakly typed and Postgres is strongly typed, for example. Using the same DBMS in dev and prod is a best practice for this reason, even if it makes your test suite run slower.