[BUG] Fixes #5010 Roar and Whirlwind don´t display a fail message

Roar and Whirlwind should now display a fail message when
used against a trainer with only one pokémon left

src/phases/move-phase.ts

@@ -368,6 +368,17 @@ export class MovePhase extends BattlePhase {
 
     const move = this.move.getMove();
 
+    // Check if the move is Roar or Whirlwind and if there is a trainer with only Pokémon left.
+    if ([Moves.ROAR, Moves.WHIRLWIND].includes(this.move.moveId) && globalScene.currentBattle.trainer) {
+      const enemyParty = globalScene.getEnemyParty();
+      // Filter out any Pokémon that are not allowed in battle (e.g. fainted ones)
+      const remainingPokemon = enemyParty.filter(pokemon => pokemon.hp > 0 && pokemon.isAllowedInBattle());
+
+      if (remainingPokemon.length <= 1) {
+        success = false;
+      }
+    }
+
     /**
      * Move conditions assume the move has a single target
      * TODO: is this sustainable?

test/moves/whirlwind.test.ts

@@ -10,6 +10,7 @@ import Phaser from "phaser";
 import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
 import { Status } from "#app/data/status-effect";
 import { StatusEffect } from "#enums/status-effect";
+import { globalScene } from "#app/global-scene";
 
 describe("Moves - Whirlwind", () => {
   let phaserGame: Phaser.Game;
@@ -156,4 +157,36 @@ describe("Moves - Whirlwind", () => {
     expect(lapras.isOnField()).toBe(true);
     expect(eevee.isOnField()).toBe(false);
   });
+
+  it("should fail when player uses Whirlwind against an opponent with only one available Pokémon", async () => {
+    // Set up the battle scenario with the player knowing Whirlwind
+    game.override.startingWave(5).enemySpecies(Species.PIDGEY).moveset([Moves.WHIRLWIND]);
+    await game.classicMode.startBattle();
+
+    const enemyParty = game.scene.getEnemyParty();
+
+    // Ensure the opponent has only one available Pokémon
+    if (enemyParty.length > 1) {
+      enemyParty.slice(1).forEach(p => {
+        p.hp = 0;
+        p.status = new Status(StatusEffect.FAINT);
+      });
+    }
+    const eligibleEnemy = enemyParty.filter(p => p.hp > 0 && p.isAllowedInBattle());
+    expect(eligibleEnemy.length).toBe(1);
+
+    // Spy on the queueMessage function
+    const queueSpy = vi.spyOn(globalScene, "queueMessage");
+
+    // Player uses Whirlwind; opponent uses Splash
+    game.move.select(Moves.WHIRLWIND);
+    await game.forceEnemyMove(Moves.SPLASH);
+    await game.phaseInterceptor.to("MoveEndPhase", false);
+    await game.toNextTurn();
+
+    // Verify that the failure message is displayed for Whirlwind
+    expect(queueSpy).toHaveBeenCalledWith(expect.stringContaining("But it failed"));
+    // Verify the opponent's Splash message
+    expect(queueSpy).toHaveBeenCalledWith(expect.stringContaining("But nothing happened!"));
+  });
 });