Test-module import failures after migrating to plone.app.testing - apparently circular imports

Question

I'm facing an issue migrating our Plone site to using plone.app.testing. I'm getting the message Test-module import failures as the first line outputted on the console.

C:\sandbox\cms.buildout>bin\test -s soschildrensvillages
Test-module import failures:

Module: soschildrensvillages.contenttypes.tests.test_portlet_concept_news

Traceback (most recent call last):
...
  File "c:\sandbox\cms.buildout\src\soschildrensvillages\soschildrensvillages\contenttypes\content\concept_folder.py", line 7, in <module>
    from plone.app.folder.folder import ATFolder
  File "c:\sandbox\cms.buildout\eggs\plone.app.folder-1.0.5-py2.7.egg\plone\app\folder\folder.py", line 4, in <module>
    from Products.ATContentTypes.interface import IATFolder
  File "c:\sandbox\cms.buildout\eggs\products.atcontenttypes-2.1.13-py2.7.egg\Products\ATContentTypes\__init__.py", line 32, in <module>
    import Products.ATContentTypes.content
  File "c:\sandbox\cms.buildout\eggs\products.atcontenttypes-2.1.13-py2.7.egg\Products\ATContentTypes\content\__init__.py", line 7, in <module>
    import Products.ATContentTypes.content.folder
  File "c:\sandbox\cms.buildout\eggs\products.atcontenttypes-2.1.13-py2.7.egg\Products\ATContentTypes\content\folder.py", line 19, in <module>
    from plone.app.folder import folder
ImportError: cannot import name folder

There are more import errors as it tries to set-up testing layers and run tests. Only the unit tests (plain TestCase) run without error.

These errors only started appearing after I migrated the last test from Products.PloneTestCase and including the following line in our testing.py module solves the issue.

from Products.PloneTestCase import PloneTestCase as ptc

I'm not sure what level of detail someone will need to help out here but any pointers to what I could try would be most appreciated.

Our testing.py looks like

products = ('collective.lineage', 'soschildrensvillages')


class SOSChildrenLayer(PloneWithPackageLayer):

    defaultBases = (PLONE_FIXTURE,)

    def __init__(self):
        super(SOSChildrenLayer, self).__init__(
                zcml_filename='configure.zcml', zcml_package=soschildrensvillages,
                additional_z2_products=products, gs_profile_id='soschildrensvillages:default'
        )

    def setUpZCMLFiles(self):
        super(SOSChildrenLayer, self).setUpZCMLFiles()
        self.loadZCML(name='overrides.zcml', package=soschildrensvillages)

    def tearDownZope(self, app):
        super(SOSChildrenLayer, self).tearDownZope(app)
        for product in products:
            z2.uninstallProduct(app, product)


SOS_CHILDREN_FIXTURE = SOSChildrenLayer()
SOS_CHILDREN_INTEGRATION_TESTING = IntegrationTesting(
        bases=(SOS_CHILDREN_FIXTURE,), 
        name="SOSChildren:Integration"
    )

In setup.py we have

  install_requires=[
      'setuptools',

      'collective.lineage',

      'plone.app.caching',
      'plone.app.folder',
      'plone.app.iterate',

      'quintagroup.seoptimizer',

      'rdflib',

      'soschildrensvillages.taxonomy',          
      'soschildren.contentexperiments',          

      'Products.AdvancedQuery',
      'Products.ATContentTypes',
      'Products.CMFPlone',
      'Products.CMFPlacefulWorkflow'
      # -*- Extra requirements: -*-
  ],

In configure.zcml we have

  <includeDependencies package="." />

concept_folder.py includes the definition of a Archetypes content type.

Answer 1

I fixed this by ensuring I imported something from Products.ATContentTypes before plone.app.folder in my module where the error was originating.

Before

from plone.app.folder.folder import ATFolder
from plone.app.folder.folder import ATFolderSchema
from Products.ATContentTypes.content.schemata import finalizeATCTSchema

After

from Products.ATContentTypes.content.schemata import finalizeATCTSchema
from plone.app.folder.folder import ATFolder
from plone.app.folder.folder import ATFolderSchema