This is the term, for the game titled Prototype see Prototype (game) or the Prototype wiki

A prototype is a game or piece of gaming hardware that is manufactured in small quantities for testing purposes.

Depending on what is being tested, prototypes may have a rough, unfinished appearance, and may not bear any significant resemblance to the final product at all.

Sometimes, prototypes are created for a project that is later cancelled, so they might also be referred to as vaporware, particularly with unfinished hardware projects such as the SNES CD-ROM peripheral developed by Sony.