test: add case for long co-author line

Author: JakobJingleheimer

test/rules/line-length.js

@@ -129,5 +129,36 @@ https://${'very-'.repeat(80)}-long-url.org/
     tt.end()
   })
 
+  t.test('Co-author lines', (tt) => {
+    const v = new Validator()
+    const context = new Commit({
+      sha: 'f1496de5a7d5474e39eafaafe6f79befe5883a5b',
+      author: {
+        name: 'Jacob Smith',
+        email: '[email protected]',
+        date: '2025-12-22T09:40:42Z',
+      },
+      message: `
+        fixup!: apply case-insensitive suggestion
+        Co-authored-by: Michaël Zasso <[email protected]>
+      `,
+    }, v)
+
+
+    context.report = (opts) => {
+      tt.pass('called report')
+      tt.equal(opts.id, 'line-length', 'id')
+      tt.equal(opts.string, '', 'string')
+      tt.equal(opts.level, 'pass', 'level')
+    }
+
+    Rule.validate(context, {
+      options: {
+        length: 72
+      }
+    })
+    tt.end()
+  })
+
   t.end()
 })