• QA (quality assurance) testing
• User testing (playtests, usability testing)

QA testing has nothing to do with enjoyment of the game and is all about about finding “bugs” (errors in the program code).

Playtests include real people who play the game and observation of their actions in order to find out how much their experience corresponds to what the developer had intended. Usability testing is a kind of user test that is designed to determine how convenient it is to interact with the game and all of its systems (interface, controls etc.). 

This is a prerequisite for enjoying the game, but convenience alone is not enough.

Each game designer has his own vision of a player's particular behavior, which in his mind forms a perfect game experience. It is very easy while working on a game to fantasize about the player's experience and imagine how great it would be. But people are different and evaluate the same situations differently.

Playtests help to bring the developer back to the real world and see the game with the eyes of those for whom it was created - real players, representatives of the game target audience. 

Because they are the ones whose favor (and money) developers try to earn.

Playtests allow to:

1. Make correct decisions as you create and develop your game
2. See emerging issues with your game during early stages of development
3. Understand exactly how the target audience perceives your game and why
4. Know how to change your game so that your target audience likes it more:

• create more comfortable controls;
• balance progress better;
• create more appealing graphics and sound;
• to present a story in a more interesting way;
• make tutorial more accessible;
• set motivating game goals;
• competently bring the player back to the game;
• build a better and more efficient monetization system.

And all this can be done thanks to playtests from the early stages of development long before the launch!