fix flake8 and scenario

__init__.py

@@ -4,6 +4,7 @@
 from trytond.pool import Pool
 from .invoice import *
 
+
 def register():
     Pool.register(
         Invoice,

invoice.py

@@ -1,7 +1,7 @@
 #This file is part account_invoice_taxes_required module for Tryton.
 #The COPYRIGHT file at the top level of this repository contains
 #the full copyright notices and license terms.
-from trytond.pyson import Eval
+
 from trytond.pool import Pool, PoolMeta
 
 __all__ = ['Invoice', 'InvoiceLine']

tests/scenario_invoice_taxes_required.rst

@@ -203,7 +203,7 @@ Create invoice Without Taxes::
     >>> Invoice.post([invoice.id], config.context)
     Traceback (most recent call last):
         ...
-    UserError: ('UserError', (u'Missing tax in line "Test" in invoice "1".', ''))
+    UserError: ('UserError', (u'Missing tax in line "Test" in invoice "1 Party".', ''))
     >>> invoice.reload()
     >>> invoice.state
     u'draft'