In my GitHuby life, I write tests obsessively. In my enterprisey-softwarey life I don't, because there is no sensible way to do it.
I mean we develop database heavy code. Should we never test the code running with the database? would be a poor choice since we would loose a lot of coverage.
What we did instead were transactional tests. Which means that in PostgreSQL sense that we actually use SAVEPOINTS to actually wrap our tests inside a savepoint and than rollback to the sane state and never commit anything to the database.
With DI this is fairly easy since we can just replace the database pool with a single connection that uses the pg jdbc driver which can insert these savepoints.
Test suite runs ~4 minutes (scala full compile + big test suite ~65%+ coverage (we started late)) in best cases and can be slow if we have cache misses (dependencies needs to be resolved, which is akward slow on scala, sbt)
We use elixir, so we get nice features like ecto sandbox with Async tests out of the box.