Test failures with Products.MailHost 4.10

[mauritsvanrees]

Plone 5.2.2 uses Products.MailHost 4.9. When I change the core development buildout to use 4.10, as in this PR, there are 26 failures.

• The tests on Python 2.7 are fine
• The tests on Python 3.6 fail
• The tests on Python 3.7 fail

Errors are like this:

initial_value must be str or None, not bytes

  File "/srv/python3.7/lib/python3.7/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/srv/python3.7/lib/python3.7/unittest/case.py", line 628, in run
    testMethod()
  File "/home/jenkins/workspace/pull-request-5.2-3.7/src/Products.CMFPlone/Products/CMFPlone/tests/testRegistrationTool.py", line 212, in testMailPassword
    msg = message_from_string(mails.messages[0])
  File "/srv/python3.7/lib/python3.7/email/__init__.py", line 38, in message_from_string
    return Parser(*args, **kws).parsestr(s)
  File "/srv/python3.7/lib/python3.7/email/parser.py", line 67, in parsestr
    return self.parse(StringIO(text), headersonly=headersonly)

See zopefoundation/Products.MailHost#33 and especially this comment where @d-maurer says we should fix the tests.

I see failures in these packages, so they likely need fixes:

• Products.CMFPlone PR: Fix tests with Products.MailHost 4.10. #3179
• plone.app.testing PR Fixed test failure on Python 3 with Products.MailHost 4.10. plone.app.testing#70
• plone.api PR Fixed test failures on Python 3 with Products.MailHost 4.10. plone.api#443
• plone.app.contentrules PR Fixed test failures on Python 3 with Products.MailHost 4.10. plone.app.contentrules#56
• plone.app.discussion PR Fix tests with Products.MailHost 4.10. plone.app.discussion#172
• plone.restapi PR Fix tests with Products.MailHost 4.10. plone.restapi#991

Maybe also:

• collective.mockmailhost. No action seems needed, but I opened an issue for good measure.

Help is welcome.
Probably best to use the maurits/mailhost-410 coredev branch from PR plone/buildout.coredev#679 and add branches there so we can test them all in combination.

Note that on Plone 5.2 the Python 2.7 tests pass just fine, it is only Python 3 that needs fixes.

[mauritsvanrees]

I have made a mailhost-410 branch for all above packages, added this to sources.cfg and made sure all those packages are in checkouts.cfg. This is ready for testing.

@jenkins-plone-org please run jobs

[mauritsvanrees]

All is merged. Jenkins might fail until all relevant changes have come through: they could not be done in the same second.
Let's leave this issue open until all is well on Jenkins 5.2.

[mauritsvanrees]

Jenkins is green.