Document the fact that the 'test' package is meant only for use by Python

itself and not by others.

Closes issue 9255.

Doc/library/test.rst

@@ -5,6 +5,13 @@
    :synopsis: Regression tests package containing the testing suite for Python.
 .. sectionauthor:: Brett Cannon <brett@python.org>
 
+.. note::
+    The :mod:`test` package is meant for internal use by Python only. It is
+    documented for the benefit of the core developers of Python. Any use of
+    this package outside of Python's standard library is discouraged as code
+    mentioned here can change or be removed without notice between releases of
+    Python.
+
 
 The :mod:`test` package contains all regression tests for Python as well as the
 modules :mod:`test.support` and :mod:`test.regrtest`.

Misc/NEWS

@@ -1655,6 +1655,9 @@ Build
 Documentation
 ------------
 
+- Issue 9255: Document that the 'test' package is meant for internal Python use
+  only.
+
 - A small wsgi server was added as Tools/scripts/serve.py, and is used to
   implement a local documentation server via 'make serve' in the doc directory.