diff --git a/roles/run-tempest/README.rst b/roles/run-tempest/README.rst
index a75fc31..001586e 100644
--- a/roles/run-tempest/README.rst
+++ b/roles/run-tempest/README.rst
@@ -12,6 +12,13 @@
 
    The number of parallel test processes.
 
+.. zuul:rolevar:: tempest_test_regex
+   :default: ''
+
+   A regular expression used to select the tests.
+   It works only when used with some specific tox environments
+   ('all', 'all-plugin'.)
+
 .. zuul:rolevar:: tox_venvlist
    :default: smoke