diff --git a/HACKING.rst b/HACKING.rst
index a74ff73..1083075 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -9,8 +9,8 @@
 ------------------------------
 
 - [T102] Cannot import OpenStack python clients in tempest/api tests
-- [T103] tempest/tests is deprecated
 - [T104] Scenario tests require a services decorator
+- [T105] Unit tests cannot use setUpClass
 
 Test Data/Configuration
 -----------------------
@@ -192,3 +192,15 @@
 The sample config file is autogenerated using a script. If any changes are made
 to the config variables in tempest then the sample config file must be
 regenerated. This can be done running the script: tools/generate_sample.sh
+
+Unit Tests
+----------
+Unit tests are a separate class of tests in tempest. They verify tempest
+itself, and thus have a different set of guidelines around them:
+
+1. They can not require anything running externally. All you should need to
+   run the unit tests is the git tree, python and the dependencies installed.
+   This includes running services, a config file, etc.
+
+2. The unit tests cannot use setUpClass, instead fixtures and testresources
+   should be used for shared state between tests.