I'm wanting to evolve my helioptile but I don't remember if Pokemon that evolve with stones learn their pre-evolution moves, so for Heliolisk, I want thunder but my helioptile hasn't learned that yet. Can it still learn it later? Or do I need to finish it's moveset before evolving it?
No, A Pokemon that has evolved by a stone can not learn his pre-evolution move by a Move Relearner. But Heliolisk can learn Thunder(and most other move Helioptile would learn) at level 1. So you can make it relearn Thunder(and most other moves Helioptile would learn) by Move Relearner. The only move Heliolisk can't learn(which Helioptile can) is Thunder Shock,Mud Slap,Tail Whip and Pound which is useless compared to other moves in my opinion. So you can evolve him without any fear. But in case of other Pokemon(which evolves by stone) don't evolve them without any research.