Maybe "just one little global variable" isn't too unmanageable, but that style leads to code that is useless except to its original programmer. - Bjarne Stroustrup

One of the things I really like about programming languages is that it's the perfect excuse to stick your nose into any field. So if you're interested in high energy physics and the structure of the universe, being a programmer is one of the best ways to get in there. It's probably easier than becoming a theoretical physicist.

I do not think that safety should be bought at the cost of complicating the expression of good solutions to real-life problems.

"How to test?" is a question that cannot be answered in general. "When to test?" however, does have a general answer: as early and as often as possible.