The problem can also be seen on Travis and Appveyor

https://travis-ci.org/wikimedia/pywikibot-core/jobs/113989338#L3348
https://ci.appveyor.com/project/wikimedia/pywikibot-core/build/1.0.823/job/yoy536ofag8fw46u#L4320

Seems like setting a dummy username doesnt work. I tried self.site._username = ['Not registered username', None] and got:

======================================================================
ERROR: Test Index page generator on wikisource:en
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ajk/Documents/wiki/pywikibot-core/tests/aspects.py", line 688, in wrapped_method
    func(self, key)
  File "/home/ajk/Documents/wiki/pywikibot-core/tests/proofreadpage_tests.py", line 546, in test_page_gen
    self.assertRaises(ValueError, index_page.page_gen, -1, 2)
  File "/usr/lib/python2.7/unittest/case.py", line 475, in assertRaises
    callableObj(*args, **kwargs)
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/proofreadpage.py", line 613, in page_gen
    % (start, end, 1, self.num_pages))
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/proofreadpage.py", line 471, in wrapper
    self._get_page_mappings()
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/proofreadpage.py", line 514, in _get_page_mappings
    self.purge()
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/page.py", line 1296, in purge
    return self.site.purgepages([self], **kwargs)
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/site.py", line 1300, in callee
    self.login(False)
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/site.py", line 2057, in login
    if loginMan.login(retry=True):
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/login.py", line 265, in login
    self.check_user_exists()
  File "/home/ajk/Documents/wiki/pywikibot-core/pywikibot/login.py", line 140, in check_user_exists
    % (self.username, self.site))
NoUsername: Username 'Not registered username' does not exist on wikisource:en

On further analysis, it seems as though this is not the tests fault.

en.wikisource has changed how it saves the URL we are testing: https://en.wikisource.org/wiki/Index:Popular_Science_Monthly_Volume_1.djvu
Whereas fr and de languages show it in a different way : https://de.wikisource.org/wiki/Index:Musen-Almanach_f%C3%BCr_das_Jahr_1799

The en.wikisource link does not use prp-pagequality now, because of which proofreadpage.py thinks the cached version is corrupt. Even if the username issue was not there, it would have failed with ValueError('Missing class="qualityN prp-pagequality-N" or class="new" in: <pagename>.').

This check happens in proofreadpage.IndexPage._get_page_mappings()

I'm not sure what needs to be done.
Has en.wikisource stopped using the ProofreadPage Extension ? (How do we check this ?)
If yes, do we just remove the en.wikisource test ?
If not, do we mark it to fail and create a new issue to fix the bot ?

This is a strange behavior of en.wikisource, I have not understood what triggers it, there is also a bug to track it. Can't find it now.

If you see no colors on the page, there is not prp-pagequality set.
If then you make a Null Edit (tab on top right of the page), colors will appear, as well as the prp-pagequality tag.

If then you make a Null Edit (tab on top right of the page), colors will appear, as well as the prp-pagequality tag.

Interesting. That does work.

Something I noticed: If I do a Null Edit when I'm not logged in - the colors do not reappear.

@Mpaa the related task you mentioned is here: T114318

In T128986#2128293, @AbdealiJK wrote:

@Mpaa the related task you mentioned is here: T114318

Thanks for finding the bug.

In T153093#2882015, @gerritbot wrote:

Change 327777 had a related patch set uploaded (by Mpaa):
Fix proofreadpage.purge()

https://gerrit.wikimedia.org/r/327777