Added DataLoader's specific tests

Author: flipbit03

setup.cfg

@@ -2,6 +2,10 @@
 exclude = setup.py,docs/*,*/examples/*,graphene/pyutils/*,tests
 max-line-length = 120
 
+# This is a specific ignore for Black+Flake8
+# source: https://black.readthedocs.io/en/stable/guides/using_black_with_other_tools.html#id1
+extend-ignore = E203
+
 [coverage:run]
 omit = graphene/pyutils/*,*/tests/*,graphene/types/scalars.py