You do not need to write tests for everything

"I don't write tests" is valid for small personal software projects. How about for code you're going to copyright or patent? I would say that's a bad strategy.

You write tests to make your code consistent. You also add in logging to make sure your code behaves as expected during various operating conditions. Production, testing, etc.

Your code gets better and better when it becomes more and more predictable. When your tests and logging all work as expected and the code also performs the expected tasks, it is safe to say your program is nearing completion.

I'm about to drop a monster project, so the logging is just being completed this week. This is my favorite part — finally being able to run a diagram mapper on the code to see what you actually created. This one took me 3 years to do. It could very well be my last solo project. This is part of 3 complete projects I'm releasing soon. They're all large projects — looking forward to new things afterwards.