chore: Add comment (#3169)

Author: KATO-Hiro

src/features/tasks/utils/contest-table/joi_providers.test.ts

@@ -80,7 +80,7 @@ describe('JOIFirstQualRoundProvider', () => {
   test('expects to handle invalid contest IDs gracefully', () => {
     const provider = new JOIFirstQualRoundProvider(ContestType.JOI);
 
-    expect(provider.getContestRoundLabel('invalid-id')).toBe('INVALID-ID');
+    expect(provider.getContestRoundLabel('invalid-id')).toBe('INVALID-ID'); // See: getContestNameLabel() in src/lib/utils/contest.ts
     expect(provider.getContestRoundLabel('joi2024yo1d')).toBe('2024d'); // 'd' doesn't match valid round (a|b|c)
   });