system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Agile methodologies in software testing

In general terms, how does this methodology work?
gpt
The basic concept is that you decide on details regarding implementation and testing while developing. 

In more classical methodologies you generally spend a lot of time in the beginning of a project to plan everything on a high detail before writing the first line of code.

In agile developement you make a very rough plan and decide the details as you go along. It is more of a "Try and error" method that is a lot more flexible but have some other drawbacks.