Fix bug when checking expected test output with regex=True. NFC (#17626)

The common case when expected_output is a string was not being handled
here leading the inner loop here being run on each character of the
string.

See #17589

Author: sbc100

test/common.py

@@ -1199,13 +1199,15 @@ def _build_and_run(self, filename, expected_output, args=None, output_nicerizer=
                               interleaved_output=interleaved_output)
       js_output = js_output.replace('\r\n', '\n')
       if expected_output:
+        if type(expected_output) not in [list, tuple]:
+          expected_output = [expected_output]
         try:
           if assert_identical:
             self.assertIdentical(expected_output, js_output)
           elif assert_all or len(expected_output) == 1:
             for o in expected_output:
               if regex:
-                self.assertTrue(re.search(o, js_output), 'Expected regex "%s" to match on:\n%s' % (regex, js_output))
+                self.assertTrue(re.search(o, js_output), 'Expected regex "%s" to match on:\n%s' % (o, js_output))
               else:
                 self.assertContained(o, js_output)
           else: