because every test run use a different instance of the class, I think
we don't need to clear() here.

using clear causes:
Traceback (most recent call last):
  File "/srv/slapgrid/slappart7/t/ean/soft/3216c6675c8ec7c75ba48e3939c44a66/eggs/Zope-4.8.7-py3.9.egg/Testing/ZopeTestCase/base.py", line 100, in tearDown
    self.beforeTearDown()
  File "<portal_components/test.erp5.testTradeModelLine>", line 106, in beforeTearDown
  File "/srv/slapgrid/slappart7/t/ean/shared/python3/25c3b9e7a12e170bd030a475160ea994/lib/python3.9/_collections_abc.py", line 929, in clear
    self.popitem()
  File "/srv/slapgrid/slappart7/t/ean/shared/python3/25c3b9e7a12e170bd030a475160ea994/lib/python3.9/_collections_abc.py", line 918, in popitem
    key = next(iter(self))
  File "<portal_components/test.erp5.testTradeModelLine>", line 66, in __iter__
TypeError

... because unittest.TestCase should not have an __iter__ method

This reverts commit 3145b32f.

Otherwise, ERP5 site setup fails while importing erp5_core/ToolTemplateItem/portal_transforms.xml.

/SR/parts/erp5/product/ERP5/Document/BusinessTemplate.py(930)_importFile()
    928         # FIXME: Why not use the importXML function directly? Are there any BT5s
    929         # with actual .zexp files on the wild?
--> 930         obj = connection.importFile(file_obj, customImporters=customImporters)
    931       self._objects[obj_key] = obj
    932

ipdb> file_obj
<_io.BufferedReader name='/SR/parts/erp5/product/ERP5/bootstrap/erp5_core/ToolTemplateItem/portal_transforms.xml'>
...
> /SR/develop-eggs/zodbpickle-2.0.0+slapospatched001-py3.8-linux-x86_64.egg/zodbpickle/pickle_3.py(995)decode_string()
    993                 return value
    994         else:
--> 995             return value.decode(self.encoding, self.errors)
    996
    997     def load_string(self):

ipdb> p value
b'\x00\x00\x00\x00\x00\x00\x00\x80'

otherwise we will have an Exception in Python 3 while importing a Business Template,
if a new portal type and its documents exist in the same Business Template.

while importing a content file, like *.js...

(BusinessTemplate.py)
  try:
    setattr(obj, property_name, data)
  except BrokenModified:
    obj.__Broken_state__[property_name] = data # <-- !!!
    obj._p_changed = 1

obj.__Broken_state__ access here also raises BrokenModified.

while importing an XML file...

(ZODB/broken.py)
  def __new__(class_, *args):
    result = object.__new__(class_) # <-- !!!
    result.__dict__['__Broken_newargs__'] = args
    return result

we get an exception 'TypeError: object.__new__(Portal Type) is not safe, use Base.__new__()'

workflow: provide legacy WorkflowHistoryList for backward compatibility even if WITH_LEGACY_WORKFLOW is False.

in Python 2, _aq_dynamic() returns None without try..except but it raises ValueError in Python 3.

(python 2)
> /SR/parts/erp5/product/ZSQLCatalog/Extensions/zsqlbrain.py(31)_aq_dynamic()
 31  ->   def _aq_dynamic(self, name):
 32         """Acquire an attribute from a real object.
 33         """
 34         if name.startswith('__') :
 35           return None
 36         return getattr(self.getObject(), name, None)
((Pdb)) getattr(self.getObject(), name, None)
*** ValueError: Unable to getObject from ZSQLBrain if ZSQL Method does not retrieve the `path` column from catalog table.
((Pdb)) r
--Return--
> /SR/parts/erp5/product/ZSQLCatalog/Extensions/zsqlbrain.py(36)_aq_dynamic()->None # <-- !!!