It was isort all along.

dabercro · dabercro · commit aac1d22655de · 2019-02-26T14:17:40.000-05:00
diff --git a/test/requirements.txt b/test/requirements.txt
@@ -1,4 +1,4 @@
-setuptools>=40.8.0
+isort==4.3.5
 testfixtures
 pylint
 coverage
