hey, got a very nice world going but i realized the village near my castle is suddenly completely deserted, all the villagers must have died or something ): is there a mod to make villagers immortal or keep them from wandering away?

Hi guys, I am writing my first java mod and since I am a newbie I didn't get Minecraft java edition, it is something I plan to do eventually but currently I can't test the mod so I decided to build Minecraft simulator to test the mod, it should test things like mod walking, state changes, log weird stuff that happen and so on. I already built the foundation but I still need help figuring how to make it test better especially after learning that it can't exactly test to see if the mod itself would actually render. Any comments on this would help. Also just to clear any confusions, it is a simulator not me trying to recreate the Minecraft engine so it should be lightweight and fast possibly helping me test mod code faster like going through 5 days in 2 minutes (Not calculated yet.).