diff -dupr a/src/twisted/python/test/test_setup.py b/src/twisted/python/test/test_setup.py --- a/src/twisted/python/test/test_setup.py 2017-06-04 07:32:04.000000000 +0000 +++ b/src/twisted/python/test/test_setup.py 2017-08-29 21:44:25.582904955 +0000 @@ -78,7 +78,7 @@ class OptionalDependenciesTests(TestCase Setuptools' Distribution object parses and stores its C{extras_require} argument as an attribute. """ - extras = dict(im_an_extra_dependency="thing") + extras = dict(im_an_extra_dependency=["thing"]) attrs = dict(extras_require=extras) distribution = Distribution(attrs) self.assertEqual(