Add a missing versionadded in unittest.rst.
diff --git a/Doc/library/unittest.rst b/Doc/library/unittest.rst
index d47a98f..f9db152 100644
--- a/Doc/library/unittest.rst
+++ b/Doc/library/unittest.rst
@@ -592,6 +592,8 @@
       Calling this during the a test method or :meth:`setUp` skips the current
       test.  See :ref:`unittest-skipping` for more information.
 
+      .. versionadded:: 3.1
+
 
    .. method:: debug()