Allow Tera Shell to work in Inverse battles (#10599)

data/rulesets.ts

@@ -1526,7 +1526,8 @@ export const Rulesets: import('../sim/dex-formats').FormatDataTable = {
 			// The effectiveness of Freeze Dry on Water isn't reverted
 			if (move && move.id === 'freezedry' && type === 'Water') return;
 			if (move && !this.dex.getImmunity(move, type)) return 1;
-			return -typeMod;
+			// Ignore normal effectiveness, prevents bug with Tera Shell
+			if (typeMod) return -typeMod;
 		},
 	},
 

test/sim/misc/inversebattle.js

@@ -124,4 +124,19 @@ describe('Inverse Battle', function () {
 		battle.makeChoices();
 		assert.equal(battle.p2.active[0].status, 'slp');
 	});
+
+	it(`should let Tera Shell take not very effective damage`, function () {
+		battle = common.createBattle({inverseMod: true}, [[
+			{species: 'wynaut', moves: ['wickedblow']},
+		], [
+			{species: 'Terapagos-Terastal', ability: 'terashell', moves: ['sleeptalk']},
+		]]);
+		battle.makeChoices();
+		const terapagos = battle.p2.active[0];
+		const damage = terapagos.maxhp - terapagos.hp;
+		assert.bounded(damage, [14, 16], `Tera Shell should yield not very effective damage roll, actual damage taken is ${damage}`);
+
+		battle.makeChoices();
+		assert.bounded(terapagos.maxhp - terapagos.hp - damage, [28, 33], `Tera Shell should not reduce damage, because Terapagos-Terastal was not at full HP`);
+	});
 });