I thought that a small project does not need testing...

This is an excellent and simple anecdote of someone discovering why TDD (and its siblings) is a fundamental core skill in software development.

What I really like here is that the author has provided a simple numerical explanation for the cause of his problem. Very useful.

Testing is not related to small or big code base.

A good programmer can code with automatic testing in his head, so in his view it doesn't need testing. But this is a personal supposition.