Unit tests and TDD?

Unit tests are some pieces of code to exercise the input, the output and the behaviour of your code. You can write them anytime you want.

But Test-Driven Development is a strategy to think (and write!) tests first.

Recursion

What is Recursion?

The process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called as recursive function.

Recursion is made for solving problems that can be broken down into smaller, repetitive problems. It is especially good for working on things that have many possible branches and are too complex for an iterative approach. One good example of this would be searching through a file system.