[Bug] Fixes Moody increasing and decreasing the same stat (#3694)

* Replaces selectableStats array with the proper decreaseStatArray

* Adds docs to MoodyAbAttr

* Updates docs, creates unit tests for moody

src/data/ability.ts

@@ -3299,11 +3299,25 @@ export class PostTurnLootAbAttr extends PostTurnAbAttr {
   }
 }
 
+/**
+ * Attribute used for {@linkcode Abilities.MOODY}
+ */
 export class MoodyAbAttr extends PostTurnAbAttr {
   constructor() {
     super(true);
   }
-
+  /**
+   * Randomly increases one BattleStat by 2 stages and decreases a different BattleStat by 1 stage
+   * @param {Pokemon} pokemon Pokemon that has this ability
+   * @param passive N/A
+   * @param simulated true if applying in a simulated call.
+   * @param args N/A
+   * @returns true
+   *
+   * Any BattleStats at +6 or -6 are excluded from being increased or decreased, respectively
+   * If the pokemon already has all BattleStats raised to stage 6, it will only decrease one BattleStat by 1 stage
+   * If the pokemon already has all BattleStats lowered to stage -6, it will only increase one BattleStat by 2 stages
+   */
   applyPostTurn(pokemon: Pokemon, passive: boolean, simulated: boolean, args: any[]): boolean {
     const selectableStats = [BattleStat.ATK, BattleStat.DEF, BattleStat.SPATK, BattleStat.SPDEF, BattleStat.SPD];
     const increaseStatArray = selectableStats.filter(s => pokemon.summonData.battleStats[s] < 6);
@@ -3315,7 +3329,7 @@ export class MoodyAbAttr extends PostTurnAbAttr {
       pokemon.scene.unshiftPhase(new StatChangePhase(pokemon.scene, pokemon.getBattlerIndex(), true, [increaseStat], 2));
     }
     if (!simulated && decreaseStatArray.length > 0) {
-      const decreaseStat = selectableStats[Utils.randInt(selectableStats.length)];
+      const decreaseStat = decreaseStatArray[Utils.randInt(decreaseStatArray.length)];
       pokemon.scene.unshiftPhase(new StatChangePhase(pokemon.scene, pokemon.getBattlerIndex(), true, [decreaseStat], -1));
     }
     return true;

src/test/abilities/moody.test.ts

@@ -0,0 +1,93 @@
+import { BattleStat } from "#app/data/battle-stat";
+import { Abilities } from "#enums/abilities";
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import GameManager from "#test/utils/gameManager";
+import { SPLASH_ONLY } from "#test/utils/testUtils";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+
+describe("Abilities - Moody", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  const battleStatsArray = [BattleStat.ATK, BattleStat.DEF, BattleStat.SPATK, BattleStat.SPDEF, BattleStat.SPD];
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+
+    game.override
+      .battleType("single")
+      .enemySpecies(Species.RATTATA)
+      .enemyAbility(Abilities.BALL_FETCH)
+      .enemyPassiveAbility(Abilities.HYDRATION)
+      .ability(Abilities.MOODY)
+      .enemyMoveset(SPLASH_ONLY)
+      .moveset(SPLASH_ONLY);
+  });
+
+  it(
+    "should increase one BattleStat by 2 stages and decrease a different BattleStat by 1 stage",
+    async () => {
+      await game.startBattle();
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      game.move.select(Moves.SPLASH);
+      await game.toNextTurn();
+
+      // Find the increased and decreased stats, make sure they are different.
+      const statChanges = playerPokemon.summonData.battleStats;
+      const changedStats = battleStatsArray.filter(bs => statChanges[bs] === 2 || statChanges[bs] === -1);
+
+      expect(changedStats).toBeTruthy();
+      expect(changedStats.length).toBe(2);
+      expect(changedStats[0] !== changedStats[1]).toBeTruthy();
+    });
+
+  it(
+    "should only increase one BattleStat by 2 stages if all BattleStats are at -6",
+    async () => {
+      await game.startBattle();
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      // Set all BattleStats to -6
+      battleStatsArray.forEach(bs => playerPokemon.summonData.battleStats[bs] = -6);
+
+      game.move.select(Moves.SPLASH);
+      await game.toNextTurn();
+
+      // Should increase one BattleStat by 2 (from -6, meaning it will be -4)
+      const increasedStat = battleStatsArray.filter(bs => playerPokemon.summonData.battleStats[bs] === -4);
+
+      expect(increasedStat).toBeTruthy();
+      expect(increasedStat.length).toBe(1);
+    });
+
+  it(
+    "should only decrease one BattleStat by 1 stage if all BattleStats are at 6",
+    async () => {
+      await game.startBattle();
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      // Set all BattleStats to 6
+      battleStatsArray.forEach(bs => playerPokemon.summonData.battleStats[bs] = 6);
+
+      game.move.select(Moves.SPLASH);
+      await game.toNextTurn();
+
+      // Should decrease one BattleStat by 1 (from 6, meaning it will be 5)
+      const decreasedStat = battleStatsArray.filter(bs => playerPokemon.summonData.battleStats[bs] === 5);
+      expect(decreasedStat).toBeTruthy();
+      expect(decreasedStat.length).toBe(1);
+    });
+});