diff --git a/src/stress/groupBy.ts b/src/stress/groupBy.ts
index bed1f0d..524d60d 100644
--- a/src/stress/groupBy.ts
+++ b/src/stress/groupBy.ts
@@ -3,7 +3,7 @@ import { DefaultMap } from '../collection/default-map';
 export function groupBy<T, K extends string | number | symbol>(
   values: Iterable<T>,
   keyer: (value: T) => K,
-): Record<K, T[]> {
+): Record<K, undefined | T[]> {
   return Object.fromEntries(groupByAsMap(values, keyer)) as Record<K, T[]>;
 }
 
diff --git a/src/stress/sortBy.spec.ts b/src/stress/sortBy.spec.ts
index bd34033..7cb9c36 100644
--- a/src/stress/sortBy.spec.ts
+++ b/src/stress/sortBy.spec.ts
@@ -1,6 +1,6 @@
 import { sortBy } from './sortBy';
 
-describe('orderBy', () => {
+describe('sortBy', () => {
   it('sorts value DESC by "natural" JS ordering', () => {
     expect(sortBy([2, 3, 1], (v) => v, false)).toEqual([3, 2, 1]);
     expect(sortBy([1, 1, 2], (v) => v, false)).toEqual([2, 1, 1]);