How to use the transaction.doom function in transaction

def test_abort_transaction_if_doomed(app):
    with app.test_request_context():
        db['answer'] = 42
        transaction.doom()

    with app.test_request_context():
        assert 'answer' not in db

continue
          tool._bootstrap()
          tool.__class__ = getattr(erp5.portal_type, tool.portal_type)

        if migrate:
          portal.migrateToPortalTypeClass()
          portal.portal_skins.changeSkin(None)
          TransactionalResource(tpc_finish=lambda txn:
              _bootstrapped.add(portal.id))
          LOG('ERP5Site', INFO, 'Transition successful, please update your'
              ' business templates')
        else:
          _bootstrapped.add(portal.id)
      except:
        # Required because the exception may be silently dropped by the caller.
        transaction.doom()
        LOG('ERP5Site', PANIC, "Automatic migration of type and"
            " property sheet tool failed", error=sys.exc_info())
        raise

    LOG("ERP5Type.dynamic", 0, "Resetting dynamic classes")
    try:
      for class_name, klass in inspect.getmembers(erp5.portal_type,
                                                  inspect.isclass):
        klass.restoreGhostState()

      # Clear accessor holders of ZODB Property Sheets and Portal Types
      erp5.accessor_holder.clear()
      erp5.accessor_holder.property_sheet.clear()

      for name in erp5.accessor_holder.portal_type.__dict__.keys():
        if name[0] != '_':

except AttributeError:
          pass # no Activity Tool yet

        if migrate:
          portal.migrateToPortalTypeClass()
          portal.portal_skins.changeSkin(None)
          TransactionalResource(tpc_finish=lambda txn:
              _bootstrapped.add(portal.id))
          transaction.get().note('Site migrated')
          LOG('ERP5Site', INFO, 'Transition successful, please update your'
              ' business templates')
        else:
          _bootstrapped.add(portal.id)
      except:
        # Required because the exception may be silently dropped by the caller.
        transaction.doom()
        LOG('ERP5Site', PANIC, "Automatic migration of core tools failed",
            error=True)
        raise

    LOG("ERP5Type.dynamic", 0, "Resetting dynamic classes")
    try:
      for class_name, klass in inspect.getmembers(erp5.portal_type,
                                                  inspect.isclass):
        # Zope Interface is implemented through __implements__,
        # __implemented__ (both implementedBy instances) and __provides__
        # (ClassProvides instance) attributes set on the class by
        # zope.interface.declarations.implementedByFallback.
        #
        # However both implementedBy and ClassProvides instances keep a
        # reference to the class itself, thus creating a circular references
        # preventing erp5.* classes to be GC even when not being actually used

discussion_id, user_id, P_SYSADMIN):
                role = R_ADMINISTRATOR
            if 'user_csvfile' in request.POST:
                try:
                    num_users = add_multiple_users_csv(
                        request, request.POST['user_csvfile'].file,
                        discussion_id, role,
                        request.POST.get('send_invite', False),
                        request.POST['email_subject'],
                        request.POST['text_email_message'],
                        request.POST['html_email_message'],
                        request.POST['sender_name'],
                        request.POST.get('resend_notloggedin', False))
                except Exception as e:
                    error = repr(e)
                    transaction.doom()
            else:
                error = request.localizer.translate(_('No file given.'))

    def allowed(role, permission):
        if role == R_SYSADMIN:
            return True
        return (role, permission) in disc_perms_as_set

    def has_local_role(user_id, role):
        return (user_id, role) in local_roles_as_set

    users = list(users)
    users.sort(key=order_by_domain_and_name)

    context = dict(
        get_default_context(request),

vcs_tool = context.getVcsTool()
if do_extract:
  vcs_tool.extractBT(context)

context.REQUEST.RESPONSE.setHeader('Content-Type', 'text/xml; charset=utf-8')

root = vcs_tool.getModifiedTree(show_unmodified)
if not root:
  return '''
'''

if REQUEST is not None: # XXX workaround to prevent zodb bloat (bt build)
  # This script is mostly used by javascript, we can abort the transaction
  import transaction
  transaction.doom()
return vcs_tool.treeToXML(root)