Refactor test (minor): use namedtuple for stub

sigi/test_testutils.py

@@ -1,10 +1,9 @@
-from sigi.testutils import SigiDataFixture
+from collections import namedtuple
 
+from sigi.testutils import SigiDataFixture
 
-class FieldStub(object):
 
-    def __init__(self, max_length):
+FieldStub = namedtuple('FieldStub', ['max_length'])
-        self.max_length = max_length
 
 
 def test_sigidatafixture():