Fixed #28478 -- Make DiscoverRunner skip creating unused test databases.

SimpleTestCase.databases makes it possible to determine the set of
databases required to run the discovered tests.

3 files changed, 20 insertions, 8 deletions

diff --git a/docs/releases/2.2.txt b/docs/releases/2.2.txt
index 5c488570aa..4a529f30da 100644
--- a/docs/releases/2.2.txt
+++ b/docs/releases/2.2.txt
@@ -293,6 +293,9 @@ Tests
   for older versions of SQLite because they would require expensive table
   introspection there.
 
+* :class:`~django.test.runner.DiscoverRunner` now skips the setup of databases
+  not :ref:`referenced by tests<testing-multi-db>`.
+
 URLs
 ~~~~
 
diff --git a/docs/topics/testing/advanced.txt b/docs/topics/testing/advanced.txt
index a3112fb367..0a228fc4ef 100644
--- a/docs/topics/testing/advanced.txt
+++ b/docs/topics/testing/advanced.txt
@@ -614,7 +614,7 @@ utility methods in the ``django.test.utils`` module.
     Performs global post-test teardown, such as removing instrumentation from
     the template system and restoring normal email services.
 
-.. function:: setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, **kwargs)
+.. function:: setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, aliases=None, **kwargs)
 
     Creates the test databases.
 
@@ -622,6 +622,14 @@ utility methods in the ``django.test.utils`` module.
     that have been made. This data will be provided to the
     :func:`teardown_databases` function at the conclusion of testing.
 
+    The ``aliases`` argument determines which :setting:`DATABASES` aliases test
+    databases should be setup for. If it's not provided, it defaults to all of
+    :setting:`DATABASES` aliases.
+
+    .. versionadded:: 2.2
+
+        The ``aliases`` argument was added.
+
 .. function:: teardown_databases(old_config, parallel=0, keepdb=False)
 
     Destroys the test databases, restoring pre-test conditions.
diff --git a/docs/topics/testing/tools.txt b/docs/topics/testing/tools.txt
index 12f20c0144..e656f89124 100644
--- a/docs/topics/testing/tools.txt
+++ b/docs/topics/testing/tools.txt
@@ -1134,13 +1134,14 @@ Multi-database support
 .. versionadded:: 2.2
 
 Django sets up a test database corresponding to every database that is
-defined in the :setting:`DATABASES` definition in your settings
-file. However, a big part of the time taken to run a Django TestCase
-is consumed by the call to ``flush`` that ensures that you have a
-clean database at the start of each test run. If you have multiple
-databases, multiple flushes are required (one for each database),
-which can be a time consuming activity -- especially if your tests
-don't need to test multi-database activity.
+defined in the :setting:`DATABASES` definition in your settings and referred to
+by at least one test through ``databases``.
+
+However, a big part of the time taken to run a Django ``TestCase`` is consumed
+by the call to ``flush`` that ensures that you have a clean database at the
+start of each test run. If you have multiple databases, multiple flushes are
+required (one for each database), which can be a time consuming activity --
+especially if your tests don't need to test multi-database activity.
 
 As an optimization, Django only flushes the ``default`` database at
 the start of each test run. If your setup contains multiple databases,