Loads of work to replace panics with results.

tests/common/test_step.rs

@@ -35,7 +35,7 @@ impl TestStep {
         match self {
             TestStep::SetPokemon { place, from_party } => {
                 let p = battle.parties()[from_party[0] as usize].get_pokemon(from_party[1] as usize);
-                battle.sides_mut()[place[0] as usize].set_pokemon(place[1], p);
+                battle.sides_mut()[place[0] as usize].set_pokemon(place[1], p).unwrap();
             }
             TestStep::SetMoveChoice {
                 for_pokemon,