Cloned databases for running tests in parallel.

docs/ref/django-admin.txt

@@ -1270,6 +1270,10 @@ By default ``--parallel`` runs one process per core according to
 either by providing it as the option's value, e.g. ``--parallel=4``, or by
 setting the ``DJANGO_TEST_PROCESSES`` environment variable.
 
+Each process gets its own database. You must ensure that different test cases
+don't access the same resources. For instance, test cases that touch the
+filesystem should create a temporary directory for their own use.
+
 This option requires the third-party ``tblib`` package to display tracebacks
 correctly:
 

docs/releases/1.9.txt

@@ -131,6 +131,10 @@ Running tests in parallel
 The :djadmin:`test` command now supports a :djadminopt:`--parallel` option to
 run a project's tests in multiple processes in parallel.
 
+Each process gets its own database. You must ensure that different test cases
+don't access the same resources. For instance, test cases that touch the
+filesystem should create a temporary directory for their own use.
+
 Minor features
 ~~~~~~~~~~~~~~
 
@@ -681,6 +685,10 @@ Database backend API
   before 1.0, but hasn't been overridden by any core backend in years
   and hasn't been called anywhere in Django's code or tests.
 
+* In order to support test parallelization, you must implement the
+  ``DatabaseCreation._clone_test_db()`` method. You may have to adjust
+  ``DatabaseCreation.get_test_db_clone_settings()``.
+
 Default settings that were tuples are now lists
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~