Many years ago, I took part in the development of a taxi-hailing mobile app that is still widely used today. I don’t know what kind of code they’re running now, but in those early days, the driver assignment code –if I remember it correctly– was similar in spirit to the grossly simplified example that follows. There are five levels of nested if statements in less than 30 lines of code. It doesn’t look so bad, some might say, but it’s not difficult to imagine how complicated this code can become with just a few more checks…
The fact that the loop is doing “find first driver matching these strange criteria” seems most obviously obscured by the pattern of assigning a value, then killing the loop or not. This strikes me as the part that makes the algorithm difficult to test, since it forces us to use a collection to test the intricacies of the inner conditions.
Once we isolate “find first driver matching condition” from computing the condition for each driver, I consider the rest a question of personal taste. Specification pattern, composition of filters, something like that. Whatever you find easier to follow.