test_runner: assert entry is a valid object

PR-URL: nodejs#55231
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/test_runner/test.js

@@ -560,7 +560,7 @@ class Test extends AsyncResource {
         const map = lazyFindSourceMap(this.loc.file);
         const entry = map?.findEntry(this.loc.line - 1, this.loc.column - 1);
 
-        if (entry !== undefined) {
+        if (entry?.originalSource !== undefined) {
           this.loc.line = entry.originalLine + 1;
           this.loc.column = entry.originalColumn + 1;
           this.loc.file = entry.originalSource;

test/parallel/test-runner-enable-source-maps-issue.js

@@ -0,0 +1,16 @@
+'use strict';
+require('../common');
+const assert = require('node:assert');
+const { spawnSync } = require('node:child_process');
+const { test } = require('node:test');
+const fixtures = require('../common/fixtures');
+
+test('ensures --enable-source-maps does not throw an error', () => {
+  const fixture = fixtures.path('test-runner', 'coverage', 'stdin.test.js');
+  const args = ['--enable-source-maps', fixture];
+
+  const result = spawnSync(process.execPath, args);
+
+  assert.strictEqual(result.stderr.toString(), '');
+  assert.strictEqual(result.status, 0);
+});