[Bug] Fix Truant behavior (#6171)

src/data/battler-tags.ts

@@ -2038,7 +2038,7 @@ export class TruantTag extends AbilityBattlerTag {
 
     const lastMove = pokemon.getLastXMoves()[0];
 
-    if (!lastMove) {
+    if (!lastMove || lastMove.move === MoveId.NONE) {
       // Don't interrupt move if last move was `Moves.NONE` OR no prior move was found
       return true;
     }

test/abilities/truant.test.ts

@@ -0,0 +1,72 @@
+import { getPokemonNameWithAffix } from "#app/messages";
+import { AbilityId } from "#enums/ability-id";
+import { MoveId } from "#enums/move-id";
+import { MoveResult } from "#enums/move-result";
+import { SpeciesId } from "#enums/species-id";
+import { GameManager } from "#test/test-utils/game-manager";
+import i18next from "i18next";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+
+describe("Ability - Truant", () => {
+  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
+      .battleStyle("single")
+      .criticalHits(false)
+      .moveset([MoveId.SPLASH, MoveId.TACKLE])
+      .ability(AbilityId.TRUANT)
+      .enemySpecies(SpeciesId.MAGIKARP)
+      .enemyAbility(AbilityId.BALL_FETCH)
+      .enemyMoveset(MoveId.SPLASH);
+  });
+
+  it("should loaf around and prevent using moves every other turn", async () => {
+    await game.classicMode.startBattle([SpeciesId.FEEBAS]);
+
+    const player = game.field.getPlayerPokemon();
+    const enemy = game.field.getEnemyPokemon();
+
+    // Turn 1: Splash succeeds
+    game.move.select(MoveId.SPLASH);
+    await game.toNextTurn();
+
+    expect(player.getLastXMoves(1)[0]).toEqual(
+      expect.objectContaining({ move: MoveId.SPLASH, result: MoveResult.SUCCESS }),
+    );
+
+    // Turn 2: Truant activates, cancelling tackle and displaying message
+    game.move.select(MoveId.TACKLE);
+    await game.toNextTurn();
+
+    expect(player.getLastXMoves(1)[0]).toEqual(expect.objectContaining({ move: MoveId.NONE, result: MoveResult.FAIL }));
+    expect(enemy.hp).toBe(enemy.getMaxHp());
+    expect(game.textInterceptor.logs).toContain(
+      i18next.t("battlerTags:truantLapse", {
+        pokemonNameWithAffix: getPokemonNameWithAffix(player),
+      }),
+    );
+
+    // Turn 3: Truant didn't activate, tackle worked
+    game.move.select(MoveId.TACKLE);
+    await game.toNextTurn();
+
+    expect(player.getLastXMoves(1)[0]).toEqual(
+      expect.objectContaining({ move: MoveId.TACKLE, result: MoveResult.SUCCESS }),
+    );
+    expect(enemy.hp).toBeLessThan(enemy.getMaxHp());
+  });
+});