Change output method to either accept a format function or supress logs on test environment

[f3liperamos]

The problem
Logger's output method ends with a console.log call.
Our only option, today, to test if it outputs correctly is to test if format is properly called.

Sugestion
Make output able to receive a custom format option, which I see as a better solution than next one.

or change output method to either return the formated/requested value and supress console.log on test environments