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.

2 files changed, 32 insertions, 5 deletions

diff --git a/django/test/runner.py b/django/test/runner.py
index ed969cc42f..180b6911fb 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -391,6 +391,9 @@ class ParallelTestSuite(unittest.TestSuite):
 
         return result
 
+    def __iter__(self):
+        return iter(self.subsuites)
+
 
 class DiscoverRunner:
     """A Django test runner that uses unittest2 test discovery."""
@@ -587,6 +590,27 @@ class DiscoverRunner:
     def suite_result(self, suite, result, **kwargs):
         return len(result.failures) + len(result.errors)
 
+    def _get_databases(self, suite):
+        databases = set()
+        for test in suite:
+            if isinstance(test, unittest.TestCase):
+                test_databases = getattr(test, 'databases', None)
+                if test_databases == '__all__':
+                    return set(connections)
+                if test_databases:
+                    databases.update(test_databases)
+            else:
+                databases.update(self._get_databases(test))
+        return databases
+
+    def get_databases(self, suite):
+        databases = self._get_databases(suite)
+        if self.verbosity >= 2:
+            unused_databases = [alias for alias in connections if alias not in databases]
+            if unused_databases:
+                print('Skipping setup of unused database(s): %s.' % ', '.join(sorted(unused_databases)))
+        return databases
+
     def run_tests(self, test_labels, extra_tests=None, **kwargs):
         """
         Run the unit tests for all the test labels in the provided list.
@@ -601,7 +625,8 @@ class DiscoverRunner:
         """
         self.setup_test_environment()
         suite = self.build_suite(test_labels, extra_tests)
-        old_config = self.setup_databases()
+        databases = self.get_databases(suite)
+        old_config = self.setup_databases(aliases=databases)
         run_failed = False
         try:
             self.run_checks()
diff --git a/django/test/utils.py b/django/test/utils.py
index c8965cdbb8..057969503d 100644
--- a/django/test/utils.py
+++ b/django/test/utils.py
@@ -152,9 +152,9 @@ def teardown_test_environment():
     del mail.outbox
 
 
-def setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, **kwargs):
+def setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, aliases=None, **kwargs):
     """Create the test databases."""
-    test_databases, mirrored_aliases = get_unique_databases_and_mirrors()
+    test_databases, mirrored_aliases = get_unique_databases_and_mirrors(aliases)
 
     old_names = []
 
@@ -238,7 +238,7 @@ def dependency_ordered(test_databases, dependencies):
     return ordered_test_databases
 
 
-def get_unique_databases_and_mirrors():
+def get_unique_databases_and_mirrors(aliases=None):
     """
     Figure out which databases actually need to be created.
 
@@ -250,6 +250,8 @@ def get_unique_databases_and_mirrors():
                       where all aliases share the same underlying database.
     - mirrored_aliases: mapping of mirror aliases to original aliases.
     """
+    if aliases is None:
+        aliases = connections
     mirrored_aliases = {}
     test_databases = {}
     dependencies = {}
@@ -262,7 +264,7 @@ def get_unique_databases_and_mirrors():
         if test_settings['MIRROR']:
             # If the database is marked as a test mirror, save the alias.
             mirrored_aliases[alias] = test_settings['MIRROR']
-        else:
+        elif alias in aliases:
             # Store a tuple with DB parameters that uniquely identify it.
             # If we have two aliases with the same values for that tuple,
             # we only need to create the test database once.