Update README.md

Joseph Luce · web-flow · commit c928f92bdd73 · 2018-06-23T19:44:21.000-07:00
diff --git a/testing/README.md b/testing/README.md
@@ -1,3 +1,4 @@
 - https://nedbatchelder.com/ 
 - http://www.diveintopython.net/unit_testing/index.html
 - https://www.youtube.com/watch?v=1Lfv5tUGsn8&index=30&list=PLi01XoE8jYohWFPpC17Z-wWhPOSuh8Er-
+- https://jeffknupp.com/blog/2013/12/09/improve-your-python-understanding-unit-testing/
