I usually create a "test room" that has events which warp you to various parts of the game and set the appropriate switches/variables/character levels so you can play there as if you had played the game to that point.
Precisely,
Do someone has an idea of how I could achieve something that would let me go directly to some part of the game ? Because if I need each time to do the whole game to just test if a little discussion box is working that won't be very productive.
PS : I don't know if that's the right section but nothing seemed more appropriate.
What I have within my own project is a map I call the "Test Arena", think of it as my developer backdoor into my game world.
I have all of my game characters, (see how they look within the game), all of the enemies (same as well as having them link to individual troops so I can see how the individual monsters specifically behave outside of normal troops especially at different levels), points that will teleport me to different maps; as well as various weapons, armors, & items.
All you need to have is an item that will teleport you back to that "Test Arena", & if you're testing anything that involves conditions based on variables, create an item that is a nonconsumable that will increase that variable by a set amount. For example variable "X" increases by 1, each time you complete a side quest. Once "X" reaches 5 event "Y", once "X" reaches 10 event "Z" happens. So create an item that increases "X" by 5 each time you use it, or by just one depending upon the numbers tied to events, & how many times you utilize variable X for game progression.
The only thing you need to make sure of, is that when release the game to someone to test, demo, whatever, that you make sure no one can get to that map, which is why I have reachable only by a specific item, I remove the item, I effectively remove the "Test Arena". You've probably seen a few Youtube videos where people have gotten into another game's version of the "Test Arena", & suddenly they have access to every weapon, armor, spell, item, location, etcetera.
I also have a collection of dungeons, only reachable through the "Test Arena" that I experiment with, so that I can tweak & balance, without messing with individual maps until I am satisfied that I've found the right settings.