Add test for duration with both months and minutes (P1M2DT3M30S)

Co-authored-by: francinelucca <[email protected]>

Author: Copilot

src/duration-format-ponyfill.ts

@@ -114,7 +114,7 @@ export default class DurationFormat {
       let formattedValue = new Intl.NumberFormat(locale, nfOpts).format(value)
 
       // Custom handling for narrow month formatting to use "mo" instead of "m"
-      if (unit === 'months' && unitStyle === 'narrow') {
+      if (unit === 'months' && (unitStyle === 'narrow' || (style === 'narrow' && formattedValue.endsWith('m')))) {
         formattedValue = formattedValue.replace(/(\d+)m$/, '$1mo')
       }
 

test/duration-format-ponyfill.ts

@@ -92,6 +92,20 @@ suite('duration format ponyfill', function () {
         {type: 'element', value: '8s'},
       ],
     },
+    {
+      duration: 'P1M2DT3M30S',
+      locale: 'en',
+      style: 'narrow',
+      parts: [
+        {type: 'element', value: '1mo'},
+        {type: 'literal', value: ' '},
+        {type: 'element', value: '2d'},
+        {type: 'literal', value: ' '},
+        {type: 'element', value: '3m'},
+        {type: 'literal', value: ' '},
+        {type: 'element', value: '30s'},
+      ],
+    },
   ])
 
   for (const {duration, locale, parts, ...opts} of tests) {