doc: add test:coverage event to custom reporter examples

PR-URL: #46752
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/test.md

@@ -555,6 +555,11 @@ const customReporter = new Transform({
       case 'test:diagnostic':
         callback(null, event.data.message);
         break;
+      case 'test:coverage': {
+        const { totalLineCount } = event.data.summary.totals;
+        callback(null, `total line count: ${totalLineCount}\n`);
+        break;
+      }
     }
   },
 });
@@ -584,6 +589,11 @@ const customReporter = new Transform({
       case 'test:diagnostic':
         callback(null, event.data.message);
         break;
+      case 'test:coverage': {
+        const { totalLineCount } = event.data.summary.totals;
+        callback(null, `total line count: ${totalLineCount}\n`);
+        break;
+      }
     }
   },
 });
@@ -612,6 +622,11 @@ export default async function * customReporter(source) {
       case 'test:diagnostic':
         yield `${event.data.message}\n`;
         break;
+      case 'test:coverage': {
+        const { totalLineCount } = event.data.summary.totals;
+        yield `total line count: ${totalLineCount}\n`;
+        break;
+      }
     }
   }
 }
@@ -636,6 +651,11 @@ module.exports = async function * customReporter(source) {
       case 'test:diagnostic':
         yield `${event.data.message}\n`;
         break;
+      case 'test:coverage': {
+        const { totalLineCount } = event.data.summary.totals;
+        yield `total line count: ${totalLineCount}\n`;
+        break;
+      }
     }
   }
 };