Random Battles: Fix STAB in 4-player battles

data/mods/gen7/random-teams.ts

@@ -955,7 +955,7 @@ export class RandomGen7Teams extends RandomTeams {
 		if (this.format.gameType === 'multi') {
 			// Random Multi Battle uses doubles move pools, but Ally Switch fails in multi battles
 			const allySwitch = movePool.indexOf('allyswitch');
-			if (allySwitch !== undefined) {
+			if (allySwitch > -1) {
 				if (movePool.length > 4) {
 					this.fastPop(movePool, allySwitch);
 				} else {

data/random-teams.ts

@@ -224,6 +224,11 @@ export class RandomTeams {
 		// element at the given index with the removed element
 		// is much, much faster than using list.splice(index, 1).
 		const length = list.length;
+		if (index < 0 || index >= list.length) {
+			// sanity check
+			throw new Error(`Index ${index} out of bounds for given array`);
+		}
+
 		const element = list[index];
 		list[index] = list[length - 1];
 		list.pop();
@@ -1630,7 +1635,7 @@ export class RandomTeams {
 			// Random Multi Battle uses doubles move pools, but Ally Switch fails in multi battles
 			// Random Free-For-All also uses doubles move pools, for now
 			const allySwitch = movePool.indexOf('allyswitch');
-			if (allySwitch !== undefined) {
+			if (allySwitch > -1) {
 				if (movePool.length > 4) {
 					this.fastPop(movePool, allySwitch);
 				} else {

test/random-battles/gen8.js

@@ -3,7 +3,7 @@
  */
 'use strict';
 
-const {testSet, testNotBothMoves} = require('./tools');
+const {testSet, testNotBothMoves, testHasSTAB} = require('./tools');
 const assert = require('../assert');
 
 describe('[Gen 8] Random Battle', () => {
@@ -39,6 +39,12 @@ describe('[Gen 8] Random Doubles Battle', () => {
 			assert(set.moves.includes('bodypress'), `Melmetal should get Body Press (got ${set.moves})`);
 		});
 	});
+
+	it('should enforce STAB on Pinsir, Pikachu, and Zygarde', () => {
+		for (const pkmn of ['pinsir', 'pikachu', 'zygarde']) {
+			testHasSTAB(pkmn, options);
+		}
+	});
 });
 
 describe('[Gen 8] Random Battle (No Dmax)', () => {
@@ -47,3 +53,13 @@ describe('[Gen 8] Random Battle (No Dmax)', () => {
 
 	// const options = {format: 'gen8randombattlenodmax', isDynamax: true};
 });
+
+describe('[Gen 8] Free-for-All Random Battle', () => {
+	const options = {format: 'gen8freeforallrandombattle', isDoubles: true};
+
+	it('should enforce STAB on Pinsir, Pikachu, and Zygarde', () => {
+		for (const pkmn of ['pinsir', 'pikachu', 'zygarde']) {
+			testHasSTAB(pkmn, options);
+		}
+	});
+});

test/random-battles/tools.js

@@ -27,6 +27,23 @@ function testSet(pokemon, options, test) {
 	}
 }
 
+/**
+ * Tests that a Pokémon always gets STAB moves.
+ *
+ * @param {ID} pokemon
+ * @param {{format?: string, rounds?: number, isDoubles?: boolean, isLead?: boolean, isDynamax?: boolean}} options
+ */
+function testHasSTAB(pokemon, options) {
+	const dex = Dex.forFormat(options.format || 'gen8randombattle');
+	const types = dex.species.get(pokemon).types;
+	testSet(pokemon, options, set => {
+		assert(
+			set.moves.some(move => types.includes(dex.moves.get(move).type)),
+			`${pokemon} should have at least one STAB move (generated moveset: ${set.moves})`
+		);
+	});
+}
+
 /**
  * Tests that a Pokémon does not get two moves together.
  *
@@ -63,3 +80,4 @@ function testTeam(options, test) {
 exports.testSet = testSet;
 exports.testNotBothMoves = testNotBothMoves;
 exports.testTeam = testTeam;
+exports.testHasSTAB = testHasSTAB;