I've become jaded with "top 5" style lists recently, but this one's pretty nice. I'm doing a few "secure development" training sessions with development teams in the next week, will be referencing this for sure.

I'm not sure writing tests makes you a better developer...gives you better habits, but not sure it results in your code being better, compared to things like fixing bugs in others code and learning a new language.

The learning a new language holds true past software development - when I learned Spanish in high school, my understanding of some of the stranger forms of English (say, past participle) improved.