diff --git a/HowToWriteTests.md b/HowToWriteTests.md
index fe0bfab..f959304 100644
--- a/HowToWriteTests.md
+++ b/HowToWriteTests.md
@@ -28,11 +28,11 @@ class T(TestCase):
 Now run it!
 
 You may notice some existing tests use the `mock` module.
-We are phasing out this style of testing.
+We are phasing out this style of testing (<https://nedbatchelder.com/blog/201206/tldw_stop_mocking_start_testing.html>, <https://martinfowler.com/articles/mocksArentStubs.html>).
 Please do not use it in new tests.
 Instead, factor units and interfaces so mocks are not required.
 If that is not possible then implement units so that they don't need to be mocked and can be used in the test suite.
-If that is not possible then implement a verified fake of the required interface and use that in the test suite.
+If that is not possible then implement [a verified fake](https://pythonspeed.com/articles/verified-fakes/) of the required interface and use that in the test suite.
 
 # code coverage