Tracing code to get a look under the hood

The only way we will know that our application is working is by opening two or more browsers and using our UI to send messages. In other words, we are manually testing our code. This is fine for experimental projects such as our chat application or small projects that aren't expected to grow, but if our code is to have a longer life or be worked on by more than one person, manual testing of this kind becomes a liability. We are not going to tackle Test-driven Development (TDD) for our chat program, but we should explore another useful debugging technique called tracing.

Tracing is a practice by which we log or print key steps in the flow of a program to make what is going on under the covers visible. In the previous section, we added a log.Println call to output the address that the chat program was binding to. In this section, we are going to formalize this and write our own complete tracing package.

We are going to explore TDD practices when writing...