Adding versionadded tag

Author: amilbourne

pandas/_testing.py

@@ -701,6 +701,8 @@ def assert_index_equal(
         Whether to compare the order of index entries as well as their values.
         If True, both indexes must contain the same elements, in the same order.
         If False, both indexes must contain the same elements, but in any order.
+
+        .. versionadded:: 1.2.0
     rtol : float, default 1e-5
         Relative tolerance. Only used when check_exact is False.