https://travis-ci.org/wikimedia/pywikibot/jobs/331196015#L5369
```lang=python
======================================================================
ERROR: test_url_image (tests.proofreadpage_tests.TestProofreadPageValidSite)
Test fetching of url image of the scan of ProofreadPage.
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/travis/build/wikimedia/pywikibot/tests/proofreadpage_tests.py", line 293, in test_url_image
self.assertEqual(page.url_image, self.valid_redlink['url_image'])
File "/home/travis/build/wikimedia/pywikibot/pywikibot/proofreadpage.py", line 539, in url_image
raise ValueError('No prp-page-image src found for %s.' % self)
ValueError: No prp-page-image src found for [[wikisource:en:Page:Pywikibot test page 3.jpg]].
```