test_runner: do not error when getting fullName of root context

PR-URL: #59377
Reviewed-By: Chemi Atlow <[email protected]>
Reviewed-By: Pietro Marchini <[email protected]>
Reviewed-By: Moshe Atlow <[email protected]>

Author: Renegade334

lib/internal/test_runner/test.js

@@ -1459,6 +1459,8 @@ class Suite extends Test {
 }
 
 function getFullName(test) {
+  if (test === test.root) return test.name;
+
   let fullName = test.name;
 
   for (let t = test.parent; t !== t.root; t = t.parent) {

test/parallel/test-runner-test-fullname.js

@@ -1,7 +1,11 @@
 'use strict';
 require('../common');
 const { strictEqual } = require('node:assert');
-const { suite, test } = require('node:test');
+const { before, suite, test } = require('node:test');
+
+before((t) => {
+  strictEqual(t.fullName, '<root>');
+});
 
 suite('suite', (t) => {
   strictEqual(t.fullName, 'suite');