Make repeat abilities not stack (#4588)

If due to fusions you have the same ability as both passive and normal, it'll no longer stack with itself.

src/data/ability.ts

@@ -4623,7 +4623,7 @@ async function applyAbAttrsInternal<TAttr extends AbAttr>(
   messages: string[] = [],
 ) {
   for (const passive of [ false, true ]) {
-    if (!pokemon?.canApplyAbility(passive)) {
+    if (!pokemon?.canApplyAbility(passive) || (passive && pokemon.getPassiveAbility().id === pokemon.getAbility().id)) {
       continue;
     }
 

src/test/abilities/ability_duplication.test.ts

@@ -0,0 +1,58 @@
+import { Stat } from "#app/enums/stat";
+import { Abilities } from "#enums/abilities";
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import GameManager from "#test/utils/gameManager";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, it, expect } from "vitest";
+
+describe("Ability Duplication", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+    game.override
+      .moveset([ Moves.SPLASH ])
+      .battleType("single")
+      .ability(Abilities.HUGE_POWER)
+      .enemyAbility(Abilities.BALL_FETCH)
+      .enemyMoveset(Moves.SPLASH);
+  });
+
+  it("huge power should only be applied once if both normal and passive", async () => {
+    game.override.passiveAbility(Abilities.HUGE_POWER);
+
+    await game.classicMode.startBattle([ Species.MAGIKARP ]);
+
+    const [ magikarp ] = game.scene.getPlayerField();
+    const magikarpAttack = magikarp.getEffectiveStat(Stat.ATK);
+
+    magikarp.summonData.abilitySuppressed = true;
+
+    expect(magikarp.getEffectiveStat(Stat.ATK)).toBe(magikarpAttack / 2);
+  });
+
+  it("huge power should stack with pure power", async () => {
+    game.override.passiveAbility(Abilities.PURE_POWER);
+
+    await game.classicMode.startBattle([ Species.MAGIKARP ]);
+
+    const [ magikarp ] = game.scene.getPlayerField();
+    const magikarpAttack = magikarp.getEffectiveStat(Stat.ATK);
+
+    magikarp.summonData.abilitySuppressed = true;
+
+    expect(magikarp.getEffectiveStat(Stat.ATK)).toBe(magikarpAttack / 4);
+  });
+});