Reorganized backends tests.

21 files changed, 731 insertions, 710 deletions

diff --git a/tests/backends/base/__init__.py b/tests/backends/base/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/backends/base/__init__.py
diff --git a/tests/backends/base/test_base.py b/tests/backends/base/test_base.py
new file mode 100644
index 0000000000..15cfbb8579
--- /dev/null
+++ b/tests/backends/base/test_base.py
@@ -0,0 +1,32 @@
+from django.db import DEFAULT_DB_ALIAS, connection, connections
+from django.db.backends.base.base import BaseDatabaseWrapper
+from django.test import SimpleTestCase
+
+
+class DatabaseWrapperTests(SimpleTestCase):
+
+    def test_initialization_class_attributes(self):
+        """
+        The "initialization" class attributes like client_class and
+        creation_class should be set on the class and reflected in the
+        corresponding instance attributes of the instantiated backend.
+        """
+        conn = connections[DEFAULT_DB_ALIAS]
+        conn_class = type(conn)
+        attr_names = [
+            ('client_class', 'client'),
+            ('creation_class', 'creation'),
+            ('features_class', 'features'),
+            ('introspection_class', 'introspection'),
+            ('ops_class', 'ops'),
+            ('validation_class', 'validation'),
+        ]
+        for class_attr_name, instance_attr_name in attr_names:
+            class_attr_value = getattr(conn_class, class_attr_name)
+            self.assertIsNotNone(class_attr_value)
+            instance_attr_value = getattr(conn, instance_attr_name)
+            self.assertIsInstance(instance_attr_value, class_attr_value)
+
+    def test_initialization_display_name(self):
+        self.assertEqual(BaseDatabaseWrapper.display_name, 'unknown')
+        self.assertNotEqual(connection.display_name, 'unknown')
diff --git a/tests/backends/base/test_creation.py b/tests/backends/base/test_creation.py
new file mode 100644
index 0000000000..519b3f049c
--- /dev/null
+++ b/tests/backends/base/test_creation.py
@@ -0,0 +1,42 @@
+import copy
+
+from django.db import DEFAULT_DB_ALIAS, connections
+from django.db.backends.base.creation import (
+    TEST_DATABASE_PREFIX, BaseDatabaseCreation,
+)
+from django.test import SimpleTestCase
+
+
+class TestDbSignatureTests(SimpleTestCase):
+
+    def get_connection_copy(self):
+        # Get a copy of the default connection. (Can't use django.db.connection
+        # because it'll modify the default connection itself.)
+        test_connection = copy.copy(connections[DEFAULT_DB_ALIAS])
+        test_connection.settings_dict = copy.copy(connections[DEFAULT_DB_ALIAS].settings_dict)
+        return test_connection
+
+    def test_default_name(self):
+        # A test db name isn't set.
+        prod_name = 'hodor'
+        test_connection = self.get_connection_copy()
+        test_connection.settings_dict['NAME'] = prod_name
+        test_connection.settings_dict['TEST'] = {'NAME': None}
+        signature = BaseDatabaseCreation(test_connection).test_db_signature()
+        self.assertEqual(signature[3], TEST_DATABASE_PREFIX + prod_name)
+
+    def test_custom_test_name(self):
+        # A regular test db name is set.
+        test_name = 'hodor'
+        test_connection = self.get_connection_copy()
+        test_connection.settings_dict['TEST'] = {'NAME': test_name}
+        signature = BaseDatabaseCreation(test_connection).test_db_signature()
+        self.assertEqual(signature[3], test_name)
+
+    def test_custom_test_name_with_test_prefix(self):
+        # A test db name prefixed with TEST_DATABASE_PREFIX is set.
+        test_name = TEST_DATABASE_PREFIX + 'hodor'
+        test_connection = self.get_connection_copy()
+        test_connection.settings_dict['TEST'] = {'NAME': test_name}
+        signature = BaseDatabaseCreation(test_connection).test_db_signature()
+        self.assertEqual(signature[3], test_name)
diff --git a/tests/backends/base/test_features.py b/tests/backends/base/test_features.py
new file mode 100644
index 0000000000..831a0002a3
--- /dev/null
+++ b/tests/backends/base/test_features.py
@@ -0,0 +1,8 @@
+from django.db import connection
+from django.test import TestCase
+
+
+class TestDatabaseFeatures(TestCase):
+
+    def test_nonexistent_feature(self):
+        self.assertFalse(hasattr(connection.features, 'nonexistent'))
diff --git a/tests/backends/mysql/__init__.py b/tests/backends/mysql/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/backends/mysql/__init__.py
diff --git a/tests/backends/mysql/test_creation.py b/tests/backends/mysql/test_creation.py
new file mode 100644
index 0000000000..e3a83346fe
--- /dev/null
+++ b/tests/backends/mysql/test_creation.py
@@ -0,0 +1,45 @@
+import unittest
+from io import StringIO
+from unittest import mock
+
+from django.db import connection
+from django.db.backends.base.creation import BaseDatabaseCreation
+from django.db.backends.mysql.creation import DatabaseCreation
+from django.db.utils import DatabaseError
+from django.test import SimpleTestCase
+
+
+@unittest.skipUnless(connection.vendor == 'mysql', 'MySQL tests')
+class DatabaseCreationTests(SimpleTestCase):
+
+    def _execute_raise_database_exists(self, cursor, parameters, keepdb=False):
+        raise DatabaseError(1007, "Can't create database '%s'; database exists" % parameters['dbname'])
+
+    def _execute_raise_access_denied(self, cursor, parameters, keepdb=False):
+        raise DatabaseError(1044, "Access denied for user")
+
+    def patch_test_db_creation(self, execute_create_test_db):
+        return mock.patch.object(BaseDatabaseCreation, '_execute_create_test_db', execute_create_test_db)
+
+    @mock.patch('sys.stdout', new_callable=StringIO)
+    @mock.patch('sys.stderr', new_callable=StringIO)
+    def test_create_test_db_database_exists(self, *mocked_objects):
+        # Simulate test database creation raising "database exists"
+        creation = DatabaseCreation(connection)
+        with self.patch_test_db_creation(self._execute_raise_database_exists):
+            with mock.patch('builtins.input', return_value='no'):
+                with self.assertRaises(SystemExit):
+                    # SystemExit is raised if the user answers "no" to the
+                    # prompt asking if it's okay to delete the test database.
+                    creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
+            # "Database exists" shouldn't appear when keepdb is on
+            creation._create_test_db(verbosity=0, autoclobber=False, keepdb=True)
+
+    @mock.patch('sys.stdout', new_callable=StringIO)
+    @mock.patch('sys.stderr', new_callable=StringIO)
+    def test_create_test_db_unexpected_error(self, *mocked_objects):
+        # Simulate test database creation raising unexpected error
+        creation = DatabaseCreation(connection)
+        with self.patch_test_db_creation(self._execute_raise_access_denied):
+            with self.assertRaises(SystemExit):
+                creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
diff --git a/tests/backends/test_features.py b/tests/backends/mysql/test_features.py
index 7bd57f0423..65c897823b 100644
--- a/tests/backends/test_features.py
+++ b/tests/backends/mysql/test_features.py
@@ -4,16 +4,10 @@ from django.db import connection
 from django.test import TestCase
 
 
-class TestDatabaseFeatures(TestCase):
+@skipUnless(connection.vendor == 'mysql', 'MySQL tests')
+class TestFeatures(TestCase):
 
-    def test_nonexistent_feature(self):
-        self.assertFalse(hasattr(connection.features, 'nonexistent'))
-
-
-@skipUnless(connection.vendor == 'mysql', 'MySQL backend tests')
-class TestMySQLFeatures(TestCase):
-
-    def test_mysql_supports_transactions(self):
+    def test_supports_transactions(self):
         """
         All storage engines except MyISAM support transactions.
         """
diff --git a/tests/backends/test_mysql.py b/tests/backends/mysql/tests.py
index 298ca9265f..c9d47eb012 100644
--- a/tests/backends/test_mysql.py
+++ b/tests/backends/mysql/tests.py
@@ -14,8 +14,8 @@ def get_connection():
 
 
 @override_settings(DEBUG=True)
-@unittest.skipUnless(connection.vendor == 'mysql', 'MySQL specific test.')
-class MySQLTests(TestCase):
+@unittest.skipUnless(connection.vendor == 'mysql', 'MySQL tests')
+class IsolationLevelTests(TestCase):
 
     read_committed = 'read committed'
     repeatable_read = 'repeatable read'
diff --git a/tests/backends/oracle/__init__.py b/tests/backends/oracle/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/backends/oracle/__init__.py
diff --git a/tests/backends/oracle/test_creation.py b/tests/backends/oracle/test_creation.py
new file mode 100644
index 0000000000..1688c4efd2
--- /dev/null
+++ b/tests/backends/oracle/test_creation.py
@@ -0,0 +1,76 @@
+import unittest
+from io import StringIO
+from unittest import mock
+
+from django.db import connection
+from django.db.backends.oracle.creation import DatabaseCreation
+from django.db.utils import DatabaseError
+from django.test import TestCase
+
+
+@unittest.skipUnless(connection.vendor == 'oracle', 'Oracle tests')
+@mock.patch.object(DatabaseCreation, '_maindb_connection', return_value=connection)
+@mock.patch('sys.stdout', new_callable=StringIO)
+@mock.patch('sys.stderr', new_callable=StringIO)
+class DatabaseCreationTests(TestCase):
+
+    def _execute_raise_user_already_exists(self, cursor, statements, parameters, verbosity, allow_quiet_fail=False):
+        # Raise "user already exists" only in test user creation
+        if statements and statements[0].startswith('CREATE USER'):
+            raise DatabaseError("ORA-01920: user name 'string' conflicts with another user or role name")
+
+    def _execute_raise_tablespace_already_exists(
+        self, cursor, statements, parameters, verbosity, allow_quiet_fail=False
+    ):
+        raise DatabaseError("ORA-01543: tablespace 'string' already exists")
+
+    def _execute_raise_insufficient_privileges(
+        self, cursor, statements, parameters, verbosity, allow_quiet_fail=False
+    ):
+        raise DatabaseError("ORA-01031: insufficient privileges")
+
+    def _test_database_passwd(self):
+        # Mocked to avoid test user password changed
+        return connection.settings_dict['SAVED_PASSWORD']
+
+    def patch_execute_statements(self, execute_statements):
+        return mock.patch.object(DatabaseCreation, '_execute_statements', execute_statements)
+
+    @mock.patch.object(DatabaseCreation, '_test_user_create', return_value=False)
+    def test_create_test_db(self, *mocked_objects):
+        creation = DatabaseCreation(connection)
+        # Simulate test database creation raising "tablespace already exists"
+        with self.patch_execute_statements(self._execute_raise_tablespace_already_exists):
+            with mock.patch('builtins.input', return_value='no'):
+                with self.assertRaises(SystemExit):
+                    # SystemExit is raised if the user answers "no" to the
+                    # prompt asking if it's okay to delete the test tablespace.
+                    creation._create_test_db(verbosity=0, keepdb=False)
+            # "Tablespace already exists" error is ignored when keepdb is on
+            creation._create_test_db(verbosity=0, keepdb=True)
+        # Simulate test database creation raising unexpected error
+        with self.patch_execute_statements(self._execute_raise_insufficient_privileges):
+            with self.assertRaises(SystemExit):
+                creation._create_test_db(verbosity=0, keepdb=False)
+            with self.assertRaises(SystemExit):
+                creation._create_test_db(verbosity=0, keepdb=True)
+
+    @mock.patch.object(DatabaseCreation, '_test_database_create', return_value=False)
+    def test_create_test_user(self, *mocked_objects):
+        creation = DatabaseCreation(connection)
+        with mock.patch.object(DatabaseCreation, '_test_database_passwd', self._test_database_passwd):
+            # Simulate test user creation raising "user already exists"
+            with self.patch_execute_statements(self._execute_raise_user_already_exists):
+                with mock.patch('builtins.input', return_value='no'):
+                    with self.assertRaises(SystemExit):
+                        # SystemExit is raised if the user answers "no" to the
+                        # prompt asking if it's okay to delete the test user.
+                        creation._create_test_db(verbosity=0, keepdb=False)
+                # "User already exists" error is ignored when keepdb is on
+                creation._create_test_db(verbosity=0, keepdb=True)
+            # Simulate test user creation raising unexpected error
+            with self.patch_execute_statements(self._execute_raise_insufficient_privileges):
+                with self.assertRaises(SystemExit):
+                    creation._create_test_db(verbosity=0, keepdb=False)
+                with self.assertRaises(SystemExit):
+                    creation._create_test_db(verbosity=0, keepdb=True)
diff --git a/tests/backends/oracle/tests.py b/tests/backends/oracle/tests.py
new file mode 100644
index 0000000000..d57d91e677
--- /dev/null
+++ b/tests/backends/oracle/tests.py
@@ -0,0 +1,55 @@
+import unittest
+
+from django.db import connection
+
+
+@unittest.skipUnless(connection.vendor == 'oracle', 'Oracle tests')
+class Tests(unittest.TestCase):
+
+    def test_quote_name(self):
+        """'%' chars are escaped for query execution."""
+        name = '"SOME%NAME"'
+        quoted_name = connection.ops.quote_name(name)
+        self.assertEqual(quoted_name % (), name)
+
+    def test_dbms_session(self):
+        """A stored procedure can be called through a cursor wrapper."""
+        with connection.cursor() as cursor:
+            cursor.callproc('DBMS_SESSION.SET_IDENTIFIER', ['_django_testing!'])
+
+    def test_cursor_var(self):
+        """Cursor variables can be passed as query parameters."""
+        from django.db.backends.oracle.base import Database
+        with connection.cursor() as cursor:
+            var = cursor.var(Database.STRING)
+            cursor.execute("BEGIN %s := 'X'; END; ", [var])
+            self.assertEqual(var.getvalue(), 'X')
+
+    def test_long_string(self):
+        """Text longer than 4000 chars can be saved and read."""
+        with connection.cursor() as cursor:
+            cursor.execute('CREATE TABLE ltext ("TEXT" NCLOB)')
+            long_str = ''.join(str(x) for x in range(4000))
+            cursor.execute('INSERT INTO ltext VALUES (%s)', [long_str])
+            cursor.execute('SELECT text FROM ltext')
+            row = cursor.fetchone()
+            self.assertEqual(long_str, row[0].read())
+            cursor.execute('DROP TABLE ltext')
+
+    def test_client_encoding(self):
+        """Client encoding is set correctly."""
+        connection.ensure_connection()
+        self.assertEqual(connection.connection.encoding, 'UTF-8')
+        self.assertEqual(connection.connection.nencoding, 'UTF-8')
+
+    def test_order_of_nls_parameters(self):
+        """
+        An 'almost right' datetime works with configured NLS parameters
+        (#18465).
+        """
+        with connection.cursor() as cursor:
+            query = "select 1 from dual where '1936-12-29 00:00' < sysdate"
+            # The query succeeds without errors - pre #18465 this
+            # wasn't the case.
+            cursor.execute(query)
+            self.assertEqual(cursor.fetchone()[0], 1)
diff --git a/tests/backends/postgresql/__init__.py b/tests/backends/postgresql/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/backends/postgresql/__init__.py
diff --git a/tests/backends/postgresql/test_creation.py b/tests/backends/postgresql/test_creation.py
new file mode 100644
index 0000000000..9554e97a54
--- /dev/null
+++ b/tests/backends/postgresql/test_creation.py
@@ -0,0 +1,95 @@
+import unittest
+from contextlib import contextmanager
+from io import StringIO
+from unittest import mock
+
+from django.db import connection
+from django.db.backends.base.creation import BaseDatabaseCreation
+from django.db.utils import DatabaseError
+from django.test import SimpleTestCase
+
+try:
+    import psycopg2  # NOQA
+except ImportError:
+    pass
+else:
+    from psycopg2 import errorcodes
+    from django.db.backends.postgresql.creation import DatabaseCreation
+
+
+@unittest.skipUnless(connection.vendor == 'postgresql', 'PostgreSQL tests')
+class DatabaseCreationTests(SimpleTestCase):
+
+    @contextmanager
+    def changed_test_settings(self, **kwargs):
+        settings = connection.settings_dict['TEST']
+        saved_values = {}
+        for name in kwargs:
+            if name in settings:
+                saved_values[name] = settings[name]
+
+        for name, value in kwargs.items():
+            settings[name] = value
+        try:
+            yield
+        finally:
+            for name, value in kwargs.items():
+                if name in saved_values:
+                    settings[name] = saved_values[name]
+                else:
+                    del settings[name]
+
+    def check_sql_table_creation_suffix(self, settings, expected):
+        with self.changed_test_settings(**settings):
+            creation = DatabaseCreation(connection)
+            suffix = creation.sql_table_creation_suffix()
+            self.assertEqual(suffix, expected)
+
+    def test_sql_table_creation_suffix_with_none_settings(self):
+        settings = {'CHARSET': None, 'TEMPLATE': None}
+        self.check_sql_table_creation_suffix(settings, "")
+
+    def test_sql_table_creation_suffix_with_encoding(self):
+        settings = {'CHARSET': 'UTF8'}
+        self.check_sql_table_creation_suffix(settings, "WITH ENCODING 'UTF8'")
+
+    def test_sql_table_creation_suffix_with_template(self):
+        settings = {'TEMPLATE': 'template0'}
+        self.check_sql_table_creation_suffix(settings, 'WITH TEMPLATE "template0"')
+
+    def test_sql_table_creation_suffix_with_encoding_and_template(self):
+        settings = {'CHARSET': 'UTF8', 'TEMPLATE': 'template0'}
+        self.check_sql_table_creation_suffix(settings, '''WITH ENCODING 'UTF8' TEMPLATE "template0"''')
+
+    def _execute_raise_database_already_exists(self, cursor, parameters, keepdb=False):
+        error = DatabaseError('database %s already exists' % parameters['dbname'])
+        error.pgcode = errorcodes.DUPLICATE_DATABASE
+        raise DatabaseError() from error
+
+    def _execute_raise_permission_denied(self, cursor, parameters, keepdb=False):
+        error = DatabaseError('permission denied to create database')
+        error.pgcode = errorcodes.INSUFFICIENT_PRIVILEGE
+        raise DatabaseError() from error
+
+    def patch_test_db_creation(self, execute_create_test_db):
+        return mock.patch.object(BaseDatabaseCreation, '_execute_create_test_db', execute_create_test_db)
+
+    @mock.patch('sys.stdout', new_callable=StringIO)
+    @mock.patch('sys.stderr', new_callable=StringIO)
+    def test_create_test_db(self, *mocked_objects):
+        creation = DatabaseCreation(connection)
+        # Simulate test database creation raising "database already exists"
+        with self.patch_test_db_creation(self._execute_raise_database_already_exists):
+            with mock.patch('builtins.input', return_value='no'):
+                with self.assertRaises(SystemExit):
+                    # SystemExit is raised if the user answers "no" to the
+                    # prompt asking if it's okay to delete the test database.
+                    creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
+            # "Database already exists" error is ignored when keepdb is on
+            creation._create_test_db(verbosity=0, autoclobber=False, keepdb=True)
+        # Simulate test database creation raising unexpected error
+        with self.patch_test_db_creation(self._execute_raise_permission_denied):
+            with self.assertRaises(SystemExit):
+                creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
+            with self.assertRaises(SystemExit):
+                creation._create_test_db(verbosity=0, autoclobber=False, keepdb=True)
diff --git a/tests/backends/test_postgresql.py b/tests/backends/postgresql/test_server_side_cursors.py
index f4020f4e5c..8576686211 100644
--- a/tests/backends/test_postgresql.py
+++ b/tests/backends/postgresql/test_server_side_cursors.py
@@ -6,10 +6,10 @@ from contextlib import contextmanager
 from django.db import connection
 from django.test import TestCase
 
-from .models import Person
+from ..models import Person
 
 
-@unittest.skipUnless(connection.vendor == 'postgresql', "Test only for PostgreSQL")
+@unittest.skipUnless(connection.vendor == 'postgresql', 'PostgreSQL tests')
 class ServerSideCursorsPostgres(TestCase):
     cursor_fields = 'name, statement, is_holdable, is_binary, is_scrollable, creation_time'
     PostgresCursor = namedtuple('PostgresCursor', cursor_fields)
diff --git a/tests/backends/postgresql/tests.py b/tests/backends/postgresql/tests.py
new file mode 100644
index 0000000000..140fbbc444
--- /dev/null
+++ b/tests/backends/postgresql/tests.py
@@ -0,0 +1,147 @@
+import unittest
+import warnings
+from unittest import mock
+
+from django.db import DatabaseError, connection
+from django.test import TestCase
+
+
+@unittest.skipUnless(connection.vendor == 'postgresql', 'PostgreSQL tests')
+class Tests(TestCase):
+
+    def test_nodb_connection(self):
+        """
+        The _nodb_connection property fallbacks to the default connection
+        database when access to the 'postgres' database is not granted.
+        """
+        def mocked_connect(self):
+            if self.settings_dict['NAME'] is None:
+                raise DatabaseError()
+            return ''
+
+        nodb_conn = connection._nodb_connection
+        self.assertIsNone(nodb_conn.settings_dict['NAME'])
+
+        # Now assume the 'postgres' db isn't available
+        with warnings.catch_warnings(record=True) as w:
+            with mock.patch('django.db.backends.base.base.BaseDatabaseWrapper.connect',
+                            side_effect=mocked_connect, autospec=True):
+                warnings.simplefilter('always', RuntimeWarning)
+                nodb_conn = connection._nodb_connection
+        self.assertIsNotNone(nodb_conn.settings_dict['NAME'])
+        self.assertEqual(nodb_conn.settings_dict['NAME'], connection.settings_dict['NAME'])
+        # Check a RuntimeWarning has been emitted
+        self.assertEqual(len(w), 1)
+        self.assertEqual(w[0].message.__class__, RuntimeWarning)
+
+    def test_connect_and_rollback(self):
+        """
+        PostgreSQL shouldn't roll back SET TIME ZONE, even if the first
+        transaction is rolled back (#17062).
+        """
+        new_connection = connection.copy()
+        try:
+            # Ensure the database default time zone is different than
+            # the time zone in new_connection.settings_dict. We can
+            # get the default time zone by reset & show.
+            cursor = new_connection.cursor()
+            cursor.execute("RESET TIMEZONE")
+            cursor.execute("SHOW TIMEZONE")
+            db_default_tz = cursor.fetchone()[0]
+            new_tz = 'Europe/Paris' if db_default_tz == 'UTC' else 'UTC'
+            new_connection.close()
+
+            # Invalidate timezone name cache, because the setting_changed
+            # handler cannot know about new_connection.
+            del new_connection.timezone_name
+
+            # Fetch a new connection with the new_tz as default
+            # time zone, run a query and rollback.
+            with self.settings(TIME_ZONE=new_tz):
+                new_connection.set_autocommit(False)
+                cursor = new_connection.cursor()
+                new_connection.rollback()
+
+                # Now let's see if the rollback rolled back the SET TIME ZONE.
+                cursor.execute("SHOW TIMEZONE")
+                tz = cursor.fetchone()[0]
+                self.assertEqual(new_tz, tz)
+
+        finally:
+            new_connection.close()
+
+    def test_connect_non_autocommit(self):
+        """
+        The connection wrapper shouldn't believe that autocommit is enabled
+        after setting the time zone when AUTOCOMMIT is False (#21452).
+        """
+        new_connection = connection.copy()
+        new_connection.settings_dict['AUTOCOMMIT'] = False
+
+        try:
+            # Open a database connection.
+            new_connection.cursor()
+            self.assertFalse(new_connection.get_autocommit())
+        finally:
+            new_connection.close()
+
+    def test_connect_isolation_level(self):
+        """
+        The transaction level can be configured with
+        DATABASES ['OPTIONS']['isolation_level'].
+        """
+        import psycopg2
+        from psycopg2.extensions import (
+            ISOLATION_LEVEL_READ_COMMITTED as read_committed,
+            ISOLATION_LEVEL_SERIALIZABLE as serializable,
+        )
+        # Since this is a django.test.TestCase, a transaction is in progress
+        # and the isolation level isn't reported as 0. This test assumes that
+        # PostgreSQL is configured with the default isolation level.
+
+        # Check the level on the psycopg2 connection, not the Django wrapper.
+        default_level = read_committed if psycopg2.__version__ < '2.7' else None
+        self.assertEqual(connection.connection.isolation_level, default_level)
+
+        new_connection = connection.copy()
+        new_connection.settings_dict['OPTIONS']['isolation_level'] = serializable
+        try:
+            # Start a transaction so the isolation level isn't reported as 0.
+            new_connection.set_autocommit(False)
+            # Check the level on the psycopg2 connection, not the Django wrapper.
+            self.assertEqual(new_connection.connection.isolation_level, serializable)
+        finally:
+            new_connection.close()
+
+    def _select(self, val):
+        with connection.cursor() as cursor:
+            cursor.execute('SELECT %s', (val,))
+            return cursor.fetchone()[0]
+
+    def test_select_ascii_array(self):
+        a = ['awef']
+        b = self._select(a)
+        self.assertEqual(a[0], b[0])
+
+    def test_select_unicode_array(self):
+        a = ['ᄲawef']
+        b = self._select(a)
+        self.assertEqual(a[0], b[0])
+
+    def test_lookup_cast(self):
+        from django.db.backends.postgresql.operations import DatabaseOperations
+        do = DatabaseOperations(connection=None)
+        lookups = (
+            'iexact', 'contains', 'icontains', 'startswith', 'istartswith',
+            'endswith', 'iendswith', 'regex', 'iregex',
+        )
+        for lookup in lookups:
+            with self.subTest(lookup=lookup):
+                self.assertIn('::text', do.lookup_cast(lookup))
+
+    def test_correct_extraction_psycopg2_version(self):
+        from django.db.backends.postgresql.base import psycopg2_version
+        with mock.patch('psycopg2.__version__', '4.2.1 (dt dec pq3 ext lo64)'):
+            self.assertEqual(psycopg2_version(), (4, 2, 1))
+        with mock.patch('psycopg2.__version__', '4.2b0.dev1 (dt dec pq3 ext lo64)'):
+            self.assertEqual(psycopg2_version(), (4, 2))
diff --git a/tests/backends/sqlite/__init__.py b/tests/backends/sqlite/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/backends/sqlite/__init__.py
diff --git a/tests/backends/sqlite/tests.py b/tests/backends/sqlite/tests.py
new file mode 100644
index 0000000000..838835ccdd
--- /dev/null
+++ b/tests/backends/sqlite/tests.py
@@ -0,0 +1,138 @@
+import re
+import threading
+import unittest
+
+from django.core.exceptions import ImproperlyConfigured
+from django.db import connection
+from django.db.models import Avg, StdDev, Sum, Variance
+from django.test import (
+    TestCase, TransactionTestCase, override_settings, skipUnlessDBFeature,
+)
+
+from ..models import Item, Object, Square
+
+
+@unittest.skipUnless(connection.vendor == 'sqlite', 'SQLite tests')
+class Tests(TestCase):
+    longMessage = True
+
+    def test_autoincrement(self):
+        """
+        auto_increment fields are created with the AUTOINCREMENT keyword
+        in order to be monotonically increasing (#10164).
+        """
+        with connection.schema_editor(collect_sql=True) as editor:
+            editor.create_model(Square)
+            statements = editor.collected_sql
+        match = re.search('"id" ([^,]+),', statements[0])
+        self.assertIsNotNone(match)
+        self.assertEqual(
+            'integer NOT NULL PRIMARY KEY AUTOINCREMENT',
+            match.group(1),
+            'Wrong SQL used to create an auto-increment column on SQLite'
+        )
+
+    def test_aggregation(self):
+        """
+        Raise NotImplementedError when aggregating on date/time fields (#19360).
+        """
+        for aggregate in (Sum, Avg, Variance, StdDev):
+            with self.assertRaises(NotImplementedError):
+                Item.objects.all().aggregate(aggregate('time'))
+            with self.assertRaises(NotImplementedError):
+                Item.objects.all().aggregate(aggregate('date'))
+            with self.assertRaises(NotImplementedError):
+                Item.objects.all().aggregate(aggregate('last_modified'))
+            with self.assertRaises(NotImplementedError):
+                Item.objects.all().aggregate(
+                    **{'complex': aggregate('last_modified') + aggregate('last_modified')}
+                )
+
+    def test_memory_db_test_name(self):
+        """A named in-memory db should be allowed where supported."""
+        from django.db.backends.sqlite3.base import DatabaseWrapper
+        settings_dict = {
+            'TEST': {
+                'NAME': 'file:memorydb_test?mode=memory&cache=shared',
+            }
+        }
+        wrapper = DatabaseWrapper(settings_dict)
+        creation = wrapper.creation
+        if creation.connection.features.can_share_in_memory_db:
+            expected = creation.connection.settings_dict['TEST']['NAME']
+            self.assertEqual(creation._get_test_db_name(), expected)
+        else:
+            msg = (
+                "Using a shared memory database with `mode=memory` in the "
+                "database name is not supported in your environment, "
+                "use `:memory:` instead."
+            )
+            with self.assertRaisesMessage(ImproperlyConfigured, msg):
+                creation._get_test_db_name()
+
+
+@unittest.skipUnless(connection.vendor == 'sqlite', 'Test only for SQLite')
+@override_settings(DEBUG=True)
+class LastExecutedQueryTest(TestCase):
+
+    def test_no_interpolation(self):
+        # This shouldn't raise an exception (#17158)
+        query = "SELECT strftime('%Y', 'now');"
+        connection.cursor().execute(query)
+        self.assertEqual(connection.queries[-1]['sql'], query)
+
+    def test_parameter_quoting(self):
+        # The implementation of last_executed_queries isn't optimal. It's
+        # worth testing that parameters are quoted (#14091).
+        query = "SELECT %s"
+        params = ["\"'\\"]
+        connection.cursor().execute(query, params)
+        # Note that the single quote is repeated
+        substituted = "SELECT '\"''\\'"
+        self.assertEqual(connection.queries[-1]['sql'], substituted)
+
+    def test_large_number_of_parameters(self):
+        # If SQLITE_MAX_VARIABLE_NUMBER (default = 999) has been changed to be
+        # greater than SQLITE_MAX_COLUMN (default = 2000), last_executed_query
+        # can hit the SQLITE_MAX_COLUMN limit (#26063).
+        cursor = connection.cursor()
+        sql = "SELECT MAX(%s)" % ", ".join(["%s"] * 2001)
+        params = list(range(2001))
+        # This should not raise an exception.
+        cursor.db.ops.last_executed_query(cursor.cursor, sql, params)
+
+
+@unittest.skipUnless(connection.vendor == 'sqlite', 'SQLite tests')
+class EscapingChecks(TestCase):
+    """
+    All tests in this test case are also run with settings.DEBUG=True in
+    EscapingChecksDebug test case, to also test CursorDebugWrapper.
+    """
+    def test_parameter_escaping(self):
+        # '%s' escaping support for sqlite3 (#13648).
+        cursor = connection.cursor()
+        cursor.execute("select strftime('%s', date('now'))")
+        response = cursor.fetchall()[0][0]
+        # response should be an non-zero integer
+        self.assertTrue(int(response))
+
+
+@unittest.skipUnless(connection.vendor == 'sqlite', 'SQLite tests')
+@override_settings(DEBUG=True)
+class EscapingChecksDebug(EscapingChecks):
+    pass
+
+
+@unittest.skipUnless(connection.vendor == 'sqlite', 'SQLite tests')
+@skipUnlessDBFeature('can_share_in_memory_db')
+class ThreadSharing(TransactionTestCase):
+    available_apps = ['backends']
+
+    def test_database_sharing_in_threads(self):
+        def create_object():
+            Object.objects.create()
+        create_object()
+        thread = threading.Thread(target=create_object)
+        thread.start()
+        thread.join()
+        self.assertEqual(Object.objects.count(), 2)
diff --git a/tests/backends/test_creation.py b/tests/backends/test_creation.py
deleted file mode 100644
index 7a18a8d19b..0000000000
--- a/tests/backends/test_creation.py
+++ /dev/null
@@ -1,244 +0,0 @@
-import copy
-import unittest
-from contextlib import contextmanager
-from io import StringIO
-from unittest import mock
-
-from django.db import DEFAULT_DB_ALIAS, connection, connections
-from django.db.backends.base.creation import (
-    TEST_DATABASE_PREFIX, BaseDatabaseCreation,
-)
-from django.db.backends.mysql.creation import (
-    DatabaseCreation as MySQLDatabaseCreation,
-)
-from django.db.backends.oracle.creation import (
-    DatabaseCreation as OracleDatabaseCreation,
-)
-from django.db.utils import DatabaseError
-from django.test import SimpleTestCase, TestCase
-
-try:
-    import psycopg2  # NOQA
-except ImportError:
-    pass
-else:
-    from psycopg2 import errorcodes
-    from django.db.backends.postgresql.creation import \
-        DatabaseCreation as PostgreSQLDatabaseCreation
-
-
-class TestDbSignatureTests(SimpleTestCase):
-
-    def get_connection_copy(self):
-        # Get a copy of the default connection. (Can't use django.db.connection
-        # because it'll modify the default connection itself.)
-        test_connection = copy.copy(connections[DEFAULT_DB_ALIAS])
-        test_connection.settings_dict = copy.copy(connections[DEFAULT_DB_ALIAS].settings_dict)
-        return test_connection
-
-    def test_default_name(self):
-        # A test db name isn't set.
-        prod_name = 'hodor'
-        test_connection = self.get_connection_copy()
-        test_connection.settings_dict['NAME'] = prod_name
-        test_connection.settings_dict['TEST'] = {'NAME': None}
-        signature = BaseDatabaseCreation(test_connection).test_db_signature()
-        self.assertEqual(signature[3], TEST_DATABASE_PREFIX + prod_name)
-
-    def test_custom_test_name(self):
-        # A regular test db name is set.
-        test_name = 'hodor'
-        test_connection = self.get_connection_copy()
-        test_connection.settings_dict['TEST'] = {'NAME': test_name}
-        signature = BaseDatabaseCreation(test_connection).test_db_signature()
-        self.assertEqual(signature[3], test_name)
-
-    def test_custom_test_name_with_test_prefix(self):
-        # A test db name prefixed with TEST_DATABASE_PREFIX is set.
-        test_name = TEST_DATABASE_PREFIX + 'hodor'
-        test_connection = self.get_connection_copy()
-        test_connection.settings_dict['TEST'] = {'NAME': test_name}
-        signature = BaseDatabaseCreation(test_connection).test_db_signature()
-        self.assertEqual(signature[3], test_name)
-
-
-@unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL-specific tests")
-class PostgreSQLDatabaseCreationTests(SimpleTestCase):
-
-    @contextmanager
-    def changed_test_settings(self, **kwargs):
-        settings = connection.settings_dict['TEST']
-        saved_values = {}
-        for name in kwargs:
-            if name in settings:
-                saved_values[name] = settings[name]
-
-        for name, value in kwargs.items():
-            settings[name] = value
-        try:
-            yield
-        finally:
-            for name, value in kwargs.items():
-                if name in saved_values:
-                    settings[name] = saved_values[name]
-                else:
-                    del settings[name]
-
-    def check_sql_table_creation_suffix(self, settings, expected):
-        with self.changed_test_settings(**settings):
-            creation = PostgreSQLDatabaseCreation(connection)
-            suffix = creation.sql_table_creation_suffix()
-            self.assertEqual(suffix, expected)
-
-    def test_sql_table_creation_suffix_with_none_settings(self):
-        settings = {'CHARSET': None, 'TEMPLATE': None}
-        self.check_sql_table_creation_suffix(settings, "")
-
-    def test_sql_table_creation_suffix_with_encoding(self):
-        settings = {'CHARSET': 'UTF8'}
-        self.check_sql_table_creation_suffix(settings, "WITH ENCODING 'UTF8'")
-
-    def test_sql_table_creation_suffix_with_template(self):
-        settings = {'TEMPLATE': 'template0'}
-        self.check_sql_table_creation_suffix(settings, 'WITH TEMPLATE "template0"')
-
-    def test_sql_table_creation_suffix_with_encoding_and_template(self):
-        settings = {'CHARSET': 'UTF8', 'TEMPLATE': 'template0'}
-        self.check_sql_table_creation_suffix(settings, '''WITH ENCODING 'UTF8' TEMPLATE "template0"''')
-
-    def _execute_raise_database_already_exists(self, cursor, parameters, keepdb=False):
-        error = DatabaseError('database %s already exists' % parameters['dbname'])
-        error.pgcode = errorcodes.DUPLICATE_DATABASE
-        raise DatabaseError() from error
-
-    def _execute_raise_permission_denied(self, cursor, parameters, keepdb=False):
-        error = DatabaseError('permission denied to create database')
-        error.pgcode = errorcodes.INSUFFICIENT_PRIVILEGE
-        raise DatabaseError() from error
-
-    def patch_test_db_creation(self, execute_create_test_db):
-        return mock.patch.object(BaseDatabaseCreation, '_execute_create_test_db', execute_create_test_db)
-
-    @mock.patch('sys.stdout', new_callable=StringIO)
-    @mock.patch('sys.stderr', new_callable=StringIO)
-    def test_create_test_db(self, *mocked_objects):
-        creation = PostgreSQLDatabaseCreation(connection)
-        # Simulate test database creation raising "database already exists"
-        with self.patch_test_db_creation(self._execute_raise_database_already_exists):
-            with mock.patch('builtins.input', return_value='no'):
-                with self.assertRaises(SystemExit):
-                    # SystemExit is raised if the user answers "no" to the
-                    # prompt asking if it's okay to delete the test database.
-                    creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
-            # "Database already exists" error is ignored when keepdb is on
-            creation._create_test_db(verbosity=0, autoclobber=False, keepdb=True)
-        # Simulate test database creation raising unexpected error
-        with self.patch_test_db_creation(self._execute_raise_permission_denied):
-            with self.assertRaises(SystemExit):
-                creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
-            with self.assertRaises(SystemExit):
-                creation._create_test_db(verbosity=0, autoclobber=False, keepdb=True)
-
-
-@unittest.skipUnless(connection.vendor == 'oracle', "Oracle specific tests")
-@mock.patch.object(OracleDatabaseCreation, '_maindb_connection', return_value=connection)
-@mock.patch('sys.stdout', new_callable=StringIO)
-@mock.patch('sys.stderr', new_callable=StringIO)
-class OracleDatabaseCreationTests(TestCase):
-
-    def _execute_raise_user_already_exists(self, cursor, statements, parameters, verbosity, allow_quiet_fail=False):
-        # Raise "user already exists" only in test user creation
-        if statements and statements[0].startswith('CREATE USER'):
-            raise DatabaseError("ORA-01920: user name 'string' conflicts with another user or role name")
-
-    def _execute_raise_tablespace_already_exists(
-        self, cursor, statements, parameters, verbosity, allow_quiet_fail=False
-    ):
-        raise DatabaseError("ORA-01543: tablespace 'string' already exists")
-
-    def _execute_raise_insufficient_privileges(
-        self, cursor, statements, parameters, verbosity, allow_quiet_fail=False
-    ):
-        raise DatabaseError("ORA-01031: insufficient privileges")
-
-    def _test_database_passwd(self):
-        # Mocked to avoid test user password changed
-        return connection.settings_dict['SAVED_PASSWORD']
-
-    def patch_execute_statements(self, execute_statements):
-        return mock.patch.object(OracleDatabaseCreation, '_execute_statements', execute_statements)
-
-    @mock.patch.object(OracleDatabaseCreation, '_test_user_create', return_value=False)
-    def test_create_test_db(self, *mocked_objects):
-        creation = OracleDatabaseCreation(connection)
-        # Simulate test database creation raising "tablespace already exists"
-        with self.patch_execute_statements(self._execute_raise_tablespace_already_exists):
-            with mock.patch('builtins.input', return_value='no'):
-                with self.assertRaises(SystemExit):
-                    # SystemExit is raised if the user answers "no" to the
-                    # prompt asking if it's okay to delete the test tablespace.
-                    creation._create_test_db(verbosity=0, keepdb=False)
-            # "Tablespace already exists" error is ignored when keepdb is on
-            creation._create_test_db(verbosity=0, keepdb=True)
-        # Simulate test database creation raising unexpected error
-        with self.patch_execute_statements(self._execute_raise_insufficient_privileges):
-            with self.assertRaises(SystemExit):
-                creation._create_test_db(verbosity=0, keepdb=False)
-            with self.assertRaises(SystemExit):
-                creation._create_test_db(verbosity=0, keepdb=True)
-
-    @mock.patch.object(OracleDatabaseCreation, '_test_database_create', return_value=False)
-    def test_create_test_user(self, *mocked_objects):
-        creation = OracleDatabaseCreation(connection)
-        with mock.patch.object(OracleDatabaseCreation, '_test_database_passwd', self._test_database_passwd):
-            # Simulate test user creation raising "user already exists"
-            with self.patch_execute_statements(self._execute_raise_user_already_exists):
-                with mock.patch('builtins.input', return_value='no'):
-                    with self.assertRaises(SystemExit):
-                        # SystemExit is raised if the user answers "no" to the
-                        # prompt asking if it's okay to delete the test user.
-                        creation._create_test_db(verbosity=0, keepdb=False)
-                # "User already exists" error is ignored when keepdb is on
-                creation._create_test_db(verbosity=0, keepdb=True)
-            # Simulate test user creation raising unexpected error
-            with self.patch_execute_statements(self._execute_raise_insufficient_privileges):
-                with self.assertRaises(SystemExit):
-                    creation._create_test_db(verbosity=0, keepdb=False)
-                with self.assertRaises(SystemExit):
-                    creation._create_test_db(verbosity=0, keepdb=True)
-
-
-@unittest.skipUnless(connection.vendor == 'mysql', "MySQL specific tests")
-class MySQLDatabaseCreationTests(SimpleTestCase):
-
-    def _execute_raise_database_exists(self, cursor, parameters, keepdb=False):
-        raise DatabaseError(1007, "Can't create database '%s'; database exists" % parameters['dbname'])
-
-    def _execute_raise_access_denied(self, cursor, parameters, keepdb=False):
-        raise DatabaseError(1044, "Access denied for user")
-
-    def patch_test_db_creation(self, execute_create_test_db):
-        return mock.patch.object(BaseDatabaseCreation, '_execute_create_test_db', execute_create_test_db)
-
-    @mock.patch('sys.stdout', new_callable=StringIO)
-    @mock.patch('sys.stderr', new_callable=StringIO)
-    def test_create_test_db_database_exists(self, *mocked_objects):
-        # Simulate test database creation raising "database exists"
-        creation = MySQLDatabaseCreation(connection)
-        with self.patch_test_db_creation(self._execute_raise_database_exists):
-            with mock.patch('builtins.input', return_value='no'):
-                with self.assertRaises(SystemExit):
-                    # SystemExit is raised if the user answers "no" to the
-                    # prompt asking if it's okay to delete the test database.
-                    creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
-            # "Database exists" shouldn't appear when keepdb is on
-            creation._create_test_db(verbosity=0, autoclobber=False, keepdb=True)
-
-    @mock.patch('sys.stdout', new_callable=StringIO)
-    @mock.patch('sys.stderr', new_callable=StringIO)
-    def test_create_test_db_unexpected_error(self, *mocked_objects):
-        # Simulate test database creation raising unexpected error
-        creation = MySQLDatabaseCreation(connection)
-        with self.patch_test_db_creation(self._execute_raise_access_denied):
-            with self.assertRaises(SystemExit):
-                creation._create_test_db(verbosity=0, autoclobber=False, keepdb=False)
diff --git a/tests/backends/test_utils.py b/tests/backends/test_utils.py
index 60429c5543..2ef1e4b9f7 100644
--- a/tests/backends/test_utils.py
+++ b/tests/backends/test_utils.py
@@ -1,22 +1,11 @@
-import unittest
+"""Tests for django.db.backends.utils"""
+from decimal import Decimal, Rounded
 
-from django.core.exceptions import ImproperlyConfigured
-from django.db import connection
-from django.db.backends.utils import truncate_name
-from django.db.utils import ProgrammingError, load_backend
-from django.test import SimpleTestCase, TestCase
+from django.db.backends.utils import format_number, truncate_name
+from django.test import SimpleTestCase
 
 
-class TestLoadBackend(SimpleTestCase):
-    def test_load_backend_invalid_name(self):
-        msg = (
-            "'foo' isn't an available database backend.\n"
-            "Try using 'django.db.backends.XXX', where XXX is one of:\n"
-            "    'mysql', 'oracle', 'postgresql', 'sqlite3'"
-        )
-        with self.assertRaisesMessage(ImproperlyConfigured, msg) as cm:
-            load_backend('foo')
-        self.assertEqual(str(cm.exception.__cause__), "No module named 'foo'")
+class TestUtils(SimpleTestCase):
 
     def test_truncate_name(self):
         self.assertEqual(truncate_name('some_table', 10), 'some_table')
@@ -28,15 +17,31 @@ class TestLoadBackend(SimpleTestCase):
         self.assertEqual(truncate_name('username"."some_long_table', 10), 'username"."some_la38a')
         self.assertEqual(truncate_name('username"."some_long_table', 10, 3), 'username"."some_loa38')
 
+    def test_format_number(self):
+        def equal(value, max_d, places, result):
+            self.assertEqual(format_number(Decimal(value), max_d, places), result)
 
-@unittest.skipUnless(connection.vendor == 'postgresql', 'PostgreSQL specific tests')
-class TestDatabaseErrorWrapper(TestCase):
-    def test_reraising_backend_specific_database_exception(self):
-        cursor = connection.cursor()
-        msg = 'table "X" does not exist'
-        with self.assertRaisesMessage(ProgrammingError, msg) as cm:
-            cursor.execute('DROP TABLE "X"')
-        self.assertNotEqual(type(cm.exception), type(cm.exception.__cause__))
-        self.assertIsNotNone(cm.exception.__cause__)
-        self.assertIsNotNone(cm.exception.__cause__.pgcode)
-        self.assertIsNotNone(cm.exception.__cause__.pgerror)
+        equal('0', 12, 3, '0.000')
+        equal('0', 12, 8, '0.00000000')
+        equal('1', 12, 9, '1.000000000')
+        equal('0.00000000', 12, 8, '0.00000000')
+        equal('0.000000004', 12, 8, '0.00000000')
+        equal('0.000000008', 12, 8, '0.00000001')
+        equal('0.000000000000000000999', 10, 8, '0.00000000')
+        equal('0.1234567890', 12, 10, '0.1234567890')
+        equal('0.1234567890', 12, 9, '0.123456789')
+        equal('0.1234567890', 12, 8, '0.12345679')
+        equal('0.1234567890', 12, 5, '0.12346')
+        equal('0.1234567890', 12, 3, '0.123')
+        equal('0.1234567890', 12, 1, '0.1')
+        equal('0.1234567890', 12, 0, '0')
+        equal('0.1234567890', None, 0, '0')
+        equal('1234567890.1234567890', None, 0, '1234567890')
+        equal('1234567890.1234567890', None, 2, '1234567890.12')
+        equal('0.1234', 5, None, '0.1234')
+        equal('123.12', 5, None, '123.12')
+
+        with self.assertRaises(Rounded):
+            equal('0.1234567890', 5, None, '0.12346')
+        with self.assertRaises(Rounded):
+            equal('1234567890.1234', 5, None, '1234600000')
diff --git a/tests/backends/tests.py b/tests/backends/tests.py
index 8847b178ef..6d38625a98 100644
--- a/tests/backends/tests.py
+++ b/tests/backends/tests.py
@@ -1,13 +1,9 @@
-# Unit and doctests for specific database backends.
+"""Tests related to django.db.backends that haven't been organized."""
 import datetime
-import re
 import threading
 import unittest
 import warnings
-from decimal import Decimal, Rounded
-from unittest import mock
 
-from django.core.exceptions import ImproperlyConfigured
 from django.core.management.color import no_style
 from django.db import (
     DEFAULT_DB_ALIAS, DatabaseError, IntegrityError, connection, connections,
@@ -15,322 +11,20 @@ from django.db import (
 )
 from django.db.backends.base.base import BaseDatabaseWrapper
 from django.db.backends.signals import connection_created
-from django.db.backends.utils import CursorWrapper, format_number
-from django.db.models import Avg, StdDev, Sum, Variance
+from django.db.backends.utils import CursorWrapper
 from django.db.models.sql.constants import CURSOR
-from django.db.utils import ConnectionHandler
 from django.test import (
-    SimpleTestCase, TestCase, TransactionTestCase, override_settings,
-    skipIfDBFeature, skipUnlessDBFeature,
+    TestCase, TransactionTestCase, override_settings, skipIfDBFeature,
+    skipUnlessDBFeature,
 )
 
 from .models import (
-    Article, Item, Object, ObjectReference, Person, Post, RawData, Reporter,
+    Article, Object, ObjectReference, Person, Post, RawData, Reporter,
     ReporterProxy, SchoolClass, Square,
     VeryLongModelNameZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ,
 )
 
 
-class DatabaseWrapperTests(SimpleTestCase):
-
-    def test_initialization_class_attributes(self):
-        """
-        The "initialization" class attributes like client_class and
-        creation_class should be set on the class and reflected in the
-        corresponding instance attributes of the instantiated backend.
-        """
-        conn = connections[DEFAULT_DB_ALIAS]
-        conn_class = type(conn)
-        attr_names = [
-            ('client_class', 'client'),
-            ('creation_class', 'creation'),
-            ('features_class', 'features'),
-            ('introspection_class', 'introspection'),
-            ('ops_class', 'ops'),
-            ('validation_class', 'validation'),
-        ]
-        for class_attr_name, instance_attr_name in attr_names:
-            class_attr_value = getattr(conn_class, class_attr_name)
-            self.assertIsNotNone(class_attr_value)
-            instance_attr_value = getattr(conn, instance_attr_name)
-            self.assertIsInstance(instance_attr_value, class_attr_value)
-
-    def test_initialization_display_name(self):
-        self.assertEqual(BaseDatabaseWrapper.display_name, 'unknown')
-        self.assertNotEqual(connection.display_name, 'unknown')
-
-
-class DummyBackendTest(SimpleTestCase):
-
-    def test_no_databases(self):
-        """
-        Empty DATABASES setting default to the dummy backend.
-        """
-        DATABASES = {}
-        conns = ConnectionHandler(DATABASES)
-        self.assertEqual(conns[DEFAULT_DB_ALIAS].settings_dict['ENGINE'], 'django.db.backends.dummy')
-        with self.assertRaises(ImproperlyConfigured):
-            conns[DEFAULT_DB_ALIAS].ensure_connection()
-
-
-@unittest.skipUnless(connection.vendor == 'oracle', "Test only for Oracle")
-class OracleTests(unittest.TestCase):
-
-    def test_quote_name(self):
-        # '%' chars are escaped for query execution.
-        name = '"SOME%NAME"'
-        quoted_name = connection.ops.quote_name(name)
-        self.assertEqual(quoted_name % (), name)
-
-    def test_dbms_session(self):
-        # If the backend is Oracle, test that we can call a standard
-        # stored procedure through our cursor wrapper.
-        with connection.cursor() as cursor:
-            cursor.callproc('DBMS_SESSION.SET_IDENTIFIER', ['_django_testing!'])
-
-    def test_cursor_var(self):
-        # If the backend is Oracle, test that we can pass cursor variables
-        # as query parameters.
-        from django.db.backends.oracle.base import Database
-
-        with connection.cursor() as cursor:
-            var = cursor.var(Database.STRING)
-            cursor.execute("BEGIN %s := 'X'; END; ", [var])
-            self.assertEqual(var.getvalue(), 'X')
-
-    def test_long_string(self):
-        # If the backend is Oracle, test that we can save a text longer
-        # than 4000 chars and read it properly
-        with connection.cursor() as cursor:
-            cursor.execute('CREATE TABLE ltext ("TEXT" NCLOB)')
-            long_str = ''.join(str(x) for x in range(4000))
-            cursor.execute('INSERT INTO ltext VALUES (%s)', [long_str])
-            cursor.execute('SELECT text FROM ltext')
-            row = cursor.fetchone()
-            self.assertEqual(long_str, row[0].read())
-            cursor.execute('DROP TABLE ltext')
-
-    def test_client_encoding(self):
-        # If the backend is Oracle, test that the client encoding is set
-        # correctly.  This was broken under Cygwin prior to r14781.
-        connection.ensure_connection()
-        self.assertEqual(connection.connection.encoding, "UTF-8")
-        self.assertEqual(connection.connection.nencoding, "UTF-8")
-
-    def test_order_of_nls_parameters(self):
-        # an 'almost right' datetime should work with configured
-        # NLS parameters as per #18465.
-        with connection.cursor() as cursor:
-            query = "select 1 from dual where '1936-12-29 00:00' < sysdate"
-            # The query succeeds without errors - pre #18465 this
-            # wasn't the case.
-            cursor.execute(query)
-            self.assertEqual(cursor.fetchone()[0], 1)
-
-
-@unittest.skipUnless(connection.vendor == 'sqlite', "Test only for SQLite")
-class SQLiteTests(TestCase):
-
-    longMessage = True
-
-    def test_autoincrement(self):
-        """
-        auto_increment fields are created with the AUTOINCREMENT keyword
-        in order to be monotonically increasing. Refs #10164.
-        """
-        with connection.schema_editor(collect_sql=True) as editor:
-            editor.create_model(Square)
-            statements = editor.collected_sql
-        match = re.search('"id" ([^,]+),', statements[0])
-        self.assertIsNotNone(match)
-        self.assertEqual(
-            'integer NOT NULL PRIMARY KEY AUTOINCREMENT',
-            match.group(1),
-            "Wrong SQL used to create an auto-increment column on SQLite"
-        )
-
-    def test_aggregation(self):
-        """
-        #19360: Raise NotImplementedError when aggregating on date/time fields.
-        """
-        for aggregate in (Sum, Avg, Variance, StdDev):
-            with self.assertRaises(NotImplementedError):
-                Item.objects.all().aggregate(aggregate('time'))
-            with self.assertRaises(NotImplementedError):
-                Item.objects.all().aggregate(aggregate('date'))
-            with self.assertRaises(NotImplementedError):
-                Item.objects.all().aggregate(aggregate('last_modified'))
-            with self.assertRaises(NotImplementedError):
-                Item.objects.all().aggregate(
-                    **{'complex': aggregate('last_modified') + aggregate('last_modified')}
-                )
-
-    def test_memory_db_test_name(self):
-        """
-        A named in-memory db should be allowed where supported.
-        """
-        from django.db.backends.sqlite3.base import DatabaseWrapper
-        settings_dict = {
-            'TEST': {
-                'NAME': 'file:memorydb_test?mode=memory&cache=shared',
-            }
-        }
-        wrapper = DatabaseWrapper(settings_dict)
-        creation = wrapper.creation
-        if creation.connection.features.can_share_in_memory_db:
-            expected = creation.connection.settings_dict['TEST']['NAME']
-            self.assertEqual(creation._get_test_db_name(), expected)
-        else:
-            msg = (
-                "Using a shared memory database with `mode=memory` in the "
-                "database name is not supported in your environment, "
-                "use `:memory:` instead."
-            )
-            with self.assertRaisesMessage(ImproperlyConfigured, msg):
-                creation._get_test_db_name()
-
-
-@unittest.skipUnless(connection.vendor == 'postgresql', "Test only for PostgreSQL")
-class PostgreSQLTests(TestCase):
-
-    def test_nodb_connection(self):
-        """
-        The _nodb_connection property fallbacks to the default connection
-        database when access to the 'postgres' database is not granted.
-        """
-        def mocked_connect(self):
-            if self.settings_dict['NAME'] is None:
-                raise DatabaseError()
-            return ''
-
-        nodb_conn = connection._nodb_connection
-        self.assertIsNone(nodb_conn.settings_dict['NAME'])
-
-        # Now assume the 'postgres' db isn't available
-        with warnings.catch_warnings(record=True) as w:
-            with mock.patch('django.db.backends.base.base.BaseDatabaseWrapper.connect',
-                            side_effect=mocked_connect, autospec=True):
-                warnings.simplefilter('always', RuntimeWarning)
-                nodb_conn = connection._nodb_connection
-        self.assertIsNotNone(nodb_conn.settings_dict['NAME'])
-        self.assertEqual(nodb_conn.settings_dict['NAME'], connection.settings_dict['NAME'])
-        # Check a RuntimeWarning has been emitted
-        self.assertEqual(len(w), 1)
-        self.assertEqual(w[0].message.__class__, RuntimeWarning)
-
-    def test_connect_and_rollback(self):
-        """
-        PostgreSQL shouldn't roll back SET TIME ZONE, even if the first
-        transaction is rolled back (#17062).
-        """
-        new_connection = connection.copy()
-
-        try:
-            # Ensure the database default time zone is different than
-            # the time zone in new_connection.settings_dict. We can
-            # get the default time zone by reset & show.
-            cursor = new_connection.cursor()
-            cursor.execute("RESET TIMEZONE")
-            cursor.execute("SHOW TIMEZONE")
-            db_default_tz = cursor.fetchone()[0]
-            new_tz = 'Europe/Paris' if db_default_tz == 'UTC' else 'UTC'
-            new_connection.close()
-
-            # Invalidate timezone name cache, because the setting_changed
-            # handler cannot know about new_connection.
-            del new_connection.timezone_name
-
-            # Fetch a new connection with the new_tz as default
-            # time zone, run a query and rollback.
-            with self.settings(TIME_ZONE=new_tz):
-                new_connection.set_autocommit(False)
-                cursor = new_connection.cursor()
-                new_connection.rollback()
-
-                # Now let's see if the rollback rolled back the SET TIME ZONE.
-                cursor.execute("SHOW TIMEZONE")
-                tz = cursor.fetchone()[0]
-                self.assertEqual(new_tz, tz)
-
-        finally:
-            new_connection.close()
-
-    def test_connect_non_autocommit(self):
-        """
-        The connection wrapper shouldn't believe that autocommit is enabled
-        after setting the time zone when AUTOCOMMIT is False (#21452).
-        """
-        new_connection = connection.copy()
-        new_connection.settings_dict['AUTOCOMMIT'] = False
-
-        try:
-            # Open a database connection.
-            new_connection.cursor()
-            self.assertFalse(new_connection.get_autocommit())
-        finally:
-            new_connection.close()
-
-    def test_connect_isolation_level(self):
-        """
-        Regression test for #18130 and #24318.
-        """
-        import psycopg2
-        from psycopg2.extensions import (
-            ISOLATION_LEVEL_READ_COMMITTED as read_committed,
-            ISOLATION_LEVEL_SERIALIZABLE as serializable,
-        )
-
-        # Since this is a django.test.TestCase, a transaction is in progress
-        # and the isolation level isn't reported as 0. This test assumes that
-        # PostgreSQL is configured with the default isolation level.
-
-        # Check the level on the psycopg2 connection, not the Django wrapper.
-        default_level = read_committed if psycopg2.__version__ < '2.7' else None
-        self.assertEqual(connection.connection.isolation_level, default_level)
-
-        new_connection = connection.copy()
-        new_connection.settings_dict['OPTIONS']['isolation_level'] = serializable
-        try:
-            # Start a transaction so the isolation level isn't reported as 0.
-            new_connection.set_autocommit(False)
-            # Check the level on the psycopg2 connection, not the Django wrapper.
-            self.assertEqual(new_connection.connection.isolation_level, serializable)
-        finally:
-            new_connection.close()
-
-    def _select(self, val):
-        with connection.cursor() as cursor:
-            cursor.execute("SELECT %s", (val,))
-            return cursor.fetchone()[0]
-
-    def test_select_ascii_array(self):
-        a = ["awef"]
-        b = self._select(a)
-        self.assertEqual(a[0], b[0])
-
-    def test_select_unicode_array(self):
-        a = ["ᄲawef"]
-        b = self._select(a)
-        self.assertEqual(a[0], b[0])
-
-    def test_lookup_cast(self):
-        from django.db.backends.postgresql.operations import DatabaseOperations
-
-        do = DatabaseOperations(connection=None)
-        for lookup in ('iexact', 'contains', 'icontains', 'startswith',
-                       'istartswith', 'endswith', 'iendswith', 'regex', 'iregex'):
-            self.assertIn('::text', do.lookup_cast(lookup))
-
-    def test_correct_extraction_psycopg2_version(self):
-        from django.db.backends.postgresql.base import psycopg2_version
-
-        with mock.patch('psycopg2.__version__', '4.2.1 (dt dec pq3 ext lo64)'):
-            self.assertEqual(psycopg2_version(), (4, 2, 1))
-
-        with mock.patch('psycopg2.__version__', '4.2b0.dev1 (dt dec pq3 ext lo64)'):
-            self.assertEqual(psycopg2_version(), (4, 2))
-
-
 class DateQuotingTest(TestCase):
 
     def test_django_date_trunc(self):
@@ -379,38 +73,6 @@ class LastExecutedQueryTest(TestCase):
         last_sql = cursor.db.ops.last_executed_query(cursor, sql, params)
         self.assertIsInstance(last_sql, str)
 
-    @unittest.skipUnless(connection.vendor == 'sqlite',
-                         "This test is specific to SQLite.")
-    def test_no_interpolation_on_sqlite(self):
-        # This shouldn't raise an exception (##17158)
-        query = "SELECT strftime('%Y', 'now');"
-        connection.cursor().execute(query)
-        self.assertEqual(connection.queries[-1]['sql'], query)
-
-    @unittest.skipUnless(connection.vendor == 'sqlite',
-                         "This test is specific to SQLite.")
-    def test_parameter_quoting_on_sqlite(self):
-        # The implementation of last_executed_queries isn't optimal. It's
-        # worth testing that parameters are quoted. See #14091.
-        query = "SELECT %s"
-        params = ["\"'\\"]
-        connection.cursor().execute(query, params)
-        # Note that the single quote is repeated
-        substituted = "SELECT '\"''\\'"
-        self.assertEqual(connection.queries[-1]['sql'], substituted)
-
-    @unittest.skipUnless(connection.vendor == 'sqlite',
-                         "This test is specific to SQLite.")
-    def test_large_number_of_parameters_on_sqlite(self):
-        # If SQLITE_MAX_VARIABLE_NUMBER (default = 999) has been changed to be
-        # greater than SQLITE_MAX_COLUMN (default = 2000), last_executed_query
-        # can hit the SQLITE_MAX_COLUMN limit. See #26063.
-        cursor = connection.cursor()
-        sql = "SELECT MAX(%s)" % ", ".join(["%s"] * 2001)
-        params = list(range(2001))
-        # This should not raise an exception.
-        cursor.db.ops.last_executed_query(cursor.cursor, sql, params)
-
 
 class ParameterHandlingTest(TestCase):
 
@@ -539,16 +201,6 @@ class EscapingChecks(TestCase):
         cursor.execute("SELECT '%%', %s" + self.bare_select_suffix, ('%d',))
         self.assertEqual(cursor.fetchall()[0], ('%', '%d'))
 
-    @unittest.skipUnless(connection.vendor == 'sqlite',
-                         "This is an sqlite-specific issue")
-    def test_sqlite_parameter_escaping(self):
-        # '%s' escaping support for sqlite3 #13648
-        cursor = connection.cursor()
-        cursor.execute("select strftime('%s', date('now'))")
-        response = cursor.fetchall()[0][0]
-        # response should be an non-zero integer
-        self.assertTrue(int(response))
-
 
 @override_settings(DEBUG=True)
 class EscapingChecksDebug(EscapingChecks):
@@ -1128,76 +780,3 @@ class DBConstraintTestCase(TestCase):
         intermediary_model.objects.create(from_object_id=obj.id, to_object_id=12345)
         self.assertEqual(obj.related_objects.count(), 1)
         self.assertEqual(intermediary_model.objects.count(), 2)
-
-
-class BackendUtilTests(SimpleTestCase):
-
-    def test_format_number(self):
-        """
-        Test the format_number converter utility
-        """
-        def equal(value, max_d, places, result):
-            self.assertEqual(format_number(Decimal(value), max_d, places), result)
-
-        equal('0', 12, 3,
-              '0.000')
-        equal('0', 12, 8,
-              '0.00000000')
-        equal('1', 12, 9,
-              '1.000000000')
-        equal('0.00000000', 12, 8,
-              '0.00000000')
-        equal('0.000000004', 12, 8,
-              '0.00000000')
-        equal('0.000000008', 12, 8,
-              '0.00000001')
-        equal('0.000000000000000000999', 10, 8,
-              '0.00000000')
-        equal('0.1234567890', 12, 10,
-              '0.1234567890')
-        equal('0.1234567890', 12, 9,
-              '0.123456789')
-        equal('0.1234567890', 12, 8,
-              '0.12345679')
-        equal('0.1234567890', 12, 5,
-              '0.12346')
-        equal('0.1234567890', 12, 3,
-              '0.123')
-        equal('0.1234567890', 12, 1,
-              '0.1')
-        equal('0.1234567890', 12, 0,
-              '0')
-        equal('0.1234567890', None, 0,
-              '0')
-        equal('1234567890.1234567890', None, 0,
-              '1234567890')
-        equal('1234567890.1234567890', None, 2,
-              '1234567890.12')
-        equal('0.1234', 5, None,
-              '0.1234')
-        equal('123.12', 5, None,
-              '123.12')
-        with self.assertRaises(Rounded):
-            equal('0.1234567890', 5, None,
-                  '0.12346')
-        with self.assertRaises(Rounded):
-            equal('1234567890.1234', 5, None,
-                  '1234600000')
-
-
-@unittest.skipUnless(connection.vendor == 'sqlite', 'SQLite specific test.')
-@skipUnlessDBFeature('can_share_in_memory_db')
-class TestSqliteThreadSharing(TransactionTestCase):
-    available_apps = ['backends']
-
-    def test_database_sharing_in_threads(self):
-        def create_object():
-            Object.objects.create()
-
-        create_object()
-
-        thread = threading.Thread(target=create_object)
-        thread.start()
-        thread.join()
-
-        self.assertEqual(Object.objects.count(), 2)
diff --git a/tests/db_utils/tests.py b/tests/db_utils/tests.py
new file mode 100644
index 0000000000..2a45342df5
--- /dev/null
+++ b/tests/db_utils/tests.py
@@ -0,0 +1,49 @@
+"""Tests for django.db.utils."""
+import unittest
+
+from django.core.exceptions import ImproperlyConfigured
+from django.db import DEFAULT_DB_ALIAS, connection
+from django.db.utils import ConnectionHandler, ProgrammingError, load_backend
+from django.test import SimpleTestCase, TestCase
+
+
+class ConnectionHandlerTests(SimpleTestCase):
+
+    def test_connection_handler_no_databases(self):
+        """Empty DATABASES setting defaults to the dummy backend."""
+        DATABASES = {}
+        conns = ConnectionHandler(DATABASES)
+        self.assertEqual(conns[DEFAULT_DB_ALIAS].settings_dict['ENGINE'], 'django.db.backends.dummy')
+        msg = (
+            'settings.DATABASES is improperly configured. Please supply the '
+            'ENGINE value. Check settings documentation for more details.'
+        )
+        with self.assertRaisesMessage(ImproperlyConfigured, msg):
+            conns[DEFAULT_DB_ALIAS].ensure_connection()
+
+
+class DatabaseErrorWrapperTests(TestCase):
+
+    @unittest.skipUnless(connection.vendor == 'postgresql', 'PostgreSQL test')
+    def test_reraising_backend_specific_database_exception(self):
+        cursor = connection.cursor()
+        msg = 'table "X" does not exist'
+        with self.assertRaisesMessage(ProgrammingError, msg) as cm:
+            cursor.execute('DROP TABLE "X"')
+        self.assertNotEqual(type(cm.exception), type(cm.exception.__cause__))
+        self.assertIsNotNone(cm.exception.__cause__)
+        self.assertIsNotNone(cm.exception.__cause__.pgcode)
+        self.assertIsNotNone(cm.exception.__cause__.pgerror)
+
+
+class LoadBackendTests(SimpleTestCase):
+
+    def test_load_backend_invalid_name(self):
+        msg = (
+            "'foo' isn't an available database backend.\n"
+            "Try using 'django.db.backends.XXX', where XXX is one of:\n"
+            "    'mysql', 'oracle', 'postgresql', 'sqlite3'"
+        )
+        with self.assertRaisesMessage(ImproperlyConfigured, msg) as cm:
+            load_backend('foo')
+        self.assertEqual(str(cm.exception.__cause__), "No module named 'foo'")