Refs #28478 -- Prevented connection attempts against disallowed databases in tests.

Mocking connect as well as cursor methods makes sure an appropriate error
message is surfaced when running a subset of test attempting to access a
a disallowed database.

django/test/testcases.py

@@ -135,7 +135,7 @@ class _AssertTemplateNotUsedContext(_AssertTemplateUsedContext):
         return '%s was rendered.' % self.template_name
 
 
-class _CursorFailure:
+class _DatabaseFailure:
     def __init__(self, wrapped, message):
         self.wrapped = wrapped
         self.message = message
@@ -173,11 +173,17 @@ class SimpleTestCase(unittest.TestCase):
 
     databases = _SimpleTestCaseDatabasesDescriptor()
     _disallowed_database_msg = (
-        'Database queries are not allowed in SimpleTestCase subclasses. '
-        'Either subclass TestCase or TransactionTestCase to ensure proper '
-        'test isolation or add %(alias)r to %(test)s.databases to silence '
+        'Database %(operation)s to %(alias)r are not allowed in SimpleTestCase '
+        'subclasses. Either subclass TestCase or TransactionTestCase to ensure '
+        'proper test isolation or add %(alias)r to %(test)s.databases to silence '
         'this failure.'
     )
+    _disallowed_connection_methods = [
+        ('connect', 'connections'),
+        ('temporary_connection', 'connections'),
+        ('cursor', 'queries'),
+        ('chunked_cursor', 'queries'),
+    ]
 
     @classmethod
     def setUpClass(cls):
@@ -188,7 +194,7 @@ class SimpleTestCase(unittest.TestCase):
         if cls._modified_settings:
             cls._cls_modified_context = modify_settings(cls._modified_settings)
             cls._cls_modified_context.enable()
-        cls._add_cursor_failures()
+        cls._add_databases_failures()
 
     @classmethod
     def _validate_databases(cls):
@@ -208,31 +214,34 @@ class SimpleTestCase(unittest.TestCase):
         return frozenset(cls.databases)
 
     @classmethod
-    def _add_cursor_failures(cls):
+    def _add_databases_failures(cls):
         cls.databases = cls._validate_databases()
         for alias in connections:
             if alias in cls.databases:
                 continue
             connection = connections[alias]
-            message = cls._disallowed_database_msg % {
-                'test': '%s.%s' % (cls.__module__, cls.__qualname__),
-                'alias': alias,
-            }
-            connection.cursor = _CursorFailure(connection.cursor, message)
-            connection.chunked_cursor = _CursorFailure(connection.chunked_cursor, message)
+            for name, operation in cls._disallowed_connection_methods:
+                message = cls._disallowed_database_msg % {
+                    'test': '%s.%s' % (cls.__module__, cls.__qualname__),
+                    'alias': alias,
+                    'operation': operation,
+                }
+                method = getattr(connection, name)
+                setattr(connection, name, _DatabaseFailure(method, message))
 
     @classmethod
-    def _remove_cursor_failures(cls):
+    def _remove_databases_failures(cls):
         for alias in connections:
             if alias in cls.databases:
                 continue
             connection = connections[alias]
-            connection.cursor = connection.cursor.wrapped
-            connection.chunked_cursor = connection.chunked_cursor.wrapped
+            for name, _ in cls._disallowed_connection_methods:
+                method = getattr(connection, name)
+                setattr(connection, name, method.wrapped)
 
     @classmethod
     def tearDownClass(cls):
-        cls._remove_cursor_failures()
+        cls._remove_databases_failures()
         if hasattr(cls, '_cls_modified_context'):
             cls._cls_modified_context.disable()
             delattr(cls, '_cls_modified_context')
@@ -894,8 +903,8 @@ class TransactionTestCase(SimpleTestCase):
 
     databases = _TransactionTestCaseDatabasesDescriptor()
     _disallowed_database_msg = (
-        'Database queries to %(alias)r are not allowed in this test. Add '
-        '%(alias)r to %(test)s.databases to ensure proper test isolation '
+        'Database %(operation)s to %(alias)r are not allowed in this test. '
+        'Add %(alias)r to %(test)s.databases to ensure proper test isolation '
         'and silence this failure.'
     )
 
@@ -1121,13 +1130,13 @@ class TestCase(TransactionTestCase):
                     call_command('loaddata', *cls.fixtures, **{'verbosity': 0, 'database': db_name})
                 except Exception:
                     cls._rollback_atomics(cls.cls_atomics)
-                    cls._remove_cursor_failures()
+                    cls._remove_databases_failures()
                     raise
         try:
             cls.setUpTestData()
         except Exception:
             cls._rollback_atomics(cls.cls_atomics)
-            cls._remove_cursor_failures()
+            cls._remove_databases_failures()
             raise
 
     @classmethod

tests/test_utils/test_testcase.py

@@ -1,4 +1,4 @@
-from django.db import IntegrityError, transaction
+from django.db import IntegrityError, connections, transaction
 from django.test import TestCase, skipUnlessDBFeature
 
 from .models import Car, PossessedCar
@@ -19,6 +19,17 @@ class TestTestCase(TestCase):
         finally:
             self._rollback_atomics = rollback_atomics
 
+    def test_disallowed_database_connection(self):
+        message = (
+            "Database connections to 'other' are not allowed in this test. "
+            "Add 'other' to test_utils.test_testcase.TestTestCase.databases to "
+            "ensure proper test isolation and silence this failure."
+        )
+        with self.assertRaisesMessage(AssertionError, message):
+            connections['other'].connect()
+        with self.assertRaisesMessage(AssertionError, message):
+            connections['other'].temporary_connection()
+
     def test_disallowed_database_queries(self):
         message = (
             "Database queries to 'other' are not allowed in this test. "

tests/test_utils/tests.py

@@ -1159,11 +1159,24 @@ class TestBadSetUpTestData(TestCase):
 
 
 class DisallowedDatabaseQueriesTests(SimpleTestCase):
+    def test_disallowed_database_connections(self):
+        expected_message = (
+            "Database connections to 'default' are not allowed in SimpleTestCase "
+            "subclasses. Either subclass TestCase or TransactionTestCase to "
+            "ensure proper test isolation or add 'default' to "
+            "test_utils.tests.DisallowedDatabaseQueriesTests.databases to "
+            "silence this failure."
+        )
+        with self.assertRaisesMessage(AssertionError, expected_message):
+            connection.connect()
+        with self.assertRaisesMessage(AssertionError, expected_message):
+            connection.temporary_connection()
+
     def test_disallowed_database_queries(self):
         expected_message = (
-            "Database queries are not allowed in SimpleTestCase subclasses. "
-            "Either subclass TestCase or TransactionTestCase to ensure proper "
-            "test isolation or add 'default' to "
+            "Database queries to 'default' are not allowed in SimpleTestCase "
+            "subclasses. Either subclass TestCase or TransactionTestCase to "
+            "ensure proper test isolation or add 'default' to "
             "test_utils.tests.DisallowedDatabaseQueriesTests.databases to "
             "silence this failure."
         )
@@ -1172,9 +1185,9 @@ class DisallowedDatabaseQueriesTests(SimpleTestCase):
 
     def test_disallowed_database_chunked_cursor_queries(self):
         expected_message = (
-            "Database queries are not allowed in SimpleTestCase subclasses. "
-            "Either subclass TestCase or TransactionTestCase to ensure proper "
-            "test isolation or add 'default' to "
+            "Database queries to 'default' are not allowed in SimpleTestCase "
+            "subclasses. Either subclass TestCase or TransactionTestCase to "
+            "ensure proper test isolation or add 'default' to "
             "test_utils.tests.DisallowedDatabaseQueriesTests.databases to "
             "silence this failure."
         )