Cultural problems are hard to change. If you like your team, one option might be to simply begin testing your own code and ask people to review your work. Don't be overly optimistic, but from time to time the right person can create enormous change simply by doing the right thing and patiently explaining why it's helpful. It's likely your experience of mature engineering practices in a bigger company is largely foreign to your colleagues, and they would enjoy learning more from you, because you care about them and care about your work.

If that doesn't help, move on. Life is short and bad practices will be a drain on your energy and your long term career trajectory.