> Instead of writng tests I try to be extremely careful in coding, and keep the code size small so I continue to understand it.

Amen, brother. I feel exactly the same way. I find this approach works perfectly 99%+ of the time, and regardless, I end up spending way way less time writing and maintaining code because of it. Understand what you're doing, and why, and you reap benefits not just at the tactical momentary level, but long term and architecturally as well. Understand the codebase really well, and it's much easier to diagnose issues that happen in production or at a larger scale.