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, 63 insertions, 0 deletions

diff --git a/tests/test_runner/test_discover_runner.py b/tests/test_runner/test_discover_runner.py
index d7569fc111..caa48a852d 100644
--- a/tests/test_runner/test_discover_runner.py
+++ b/tests/test_runner/test_discover_runner.py
@@ -3,6 +3,7 @@ from argparse import ArgumentParser
 from contextlib import contextmanager
 from unittest import TestSuite, TextTestRunner, defaultTestLoader
 
+from django.db import connections
 from django.test import SimpleTestCase
 from django.test.runner import DiscoverRunner
 from django.test.utils import captured_stdout
@@ -223,3 +224,47 @@ class DiscoverRunnerTests(SimpleTestCase):
         with captured_stdout() as stdout:
             runner.build_suite(['test_runner_apps.tagged.tests'])
             self.assertIn('Excluding test tag(s): bar, foo.\n', stdout.getvalue())
+
+
+class DiscoverRunnerGetDatabasesTests(SimpleTestCase):
+    runner = DiscoverRunner(verbosity=2)
+    skip_msg = 'Skipping setup of unused database(s): '
+
+    def get_databases(self, test_labels):
+        suite = self.runner.build_suite(test_labels)
+        with captured_stdout() as stdout:
+            databases = self.runner.get_databases(suite)
+        return databases, stdout.getvalue()
+
+    def test_mixed(self):
+        databases, output = self.get_databases(['test_runner_apps.databases.tests'])
+        self.assertEqual(databases, set(connections))
+        self.assertNotIn(self.skip_msg, output)
+
+    def test_all(self):
+        databases, output = self.get_databases(['test_runner_apps.databases.tests.AllDatabasesTests'])
+        self.assertEqual(databases, set(connections))
+        self.assertNotIn(self.skip_msg, output)
+
+    def test_default_and_other(self):
+        databases, output = self.get_databases([
+            'test_runner_apps.databases.tests.DefaultDatabaseTests',
+            'test_runner_apps.databases.tests.OtherDatabaseTests',
+        ])
+        self.assertEqual(databases, set(connections))
+        self.assertNotIn(self.skip_msg, output)
+
+    def test_default_only(self):
+        databases, output = self.get_databases(['test_runner_apps.databases.tests.DefaultDatabaseTests'])
+        self.assertEqual(databases, {'default'})
+        self.assertIn(self.skip_msg + 'other', output)
+
+    def test_other_only(self):
+        databases, output = self.get_databases(['test_runner_apps.databases.tests.OtherDatabaseTests'])
+        self.assertEqual(databases, {'other'})
+        self.assertIn(self.skip_msg + 'default', output)
+
+    def test_no_databases_required(self):
+        databases, output = self.get_databases(['test_runner_apps.databases.tests.NoDatabaseTests'])
+        self.assertEqual(databases, set())
+        self.assertIn(self.skip_msg + 'default, other', output)
diff --git a/tests/test_runner_apps/databases/__init__.py b/tests/test_runner_apps/databases/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/test_runner_apps/databases/__init__.py
diff --git a/tests/test_runner_apps/databases/tests.py b/tests/test_runner_apps/databases/tests.py
new file mode 100644
index 0000000000..4be260e689
--- /dev/null
+++ b/tests/test_runner_apps/databases/tests.py
@@ -0,0 +1,18 @@
+import unittest
+
+
+class NoDatabaseTests(unittest.TestCase):
+    def test_nothing(self):
+        pass
+
+
+class DefaultDatabaseTests(NoDatabaseTests):
+    databases = {'default'}
+
+
+class OtherDatabaseTests(NoDatabaseTests):
+    databases = {'other'}
+
+
+class AllDatabasesTests(NoDatabaseTests):
+    databases = '__all__'