Also simplify a bit the code

- do not use getToolByName.
- do not put two statements on the same line
- merge nested "if" statements around a single code block

Amend 9240d498: Since many Loaders are
instanciated by unittest itself, filter_test_list still have to be a class
variable

This reverts commit 15aaafbf.
Reason: To be consistent with packing list and order until
the new way of handling payment conditions is implemented.

  This parameter has been passed always by the erp5.util implementation. Introduce
  this parameter makes the API compatible for future implementation with support
  to scalability tests even if the current code is not ready yet.

A simpler way to achieve the same fix.

Also, reuse existing local.

Writing 0 bytes or truncating past file end increases file length.

This reverts commit 6a8987fb.

The assertion was not correct when account_type/expense & account_type/income
have child categories