Added test to confirm #12583 resolution

from django.db import (connection, connections, DEFAULT_DB_ALIAS,

    DatabaseError, IntegrityError, transaction)

from django.db.backends.signals import connection_created

from django.db.backends.sqlite3.base import DatabaseOperations

from django.db.backends.postgresql_psycopg2 import version as pg_version

from django.db.backends.utils import format_number, CursorWrapper

from django.db.models import Sum, Avg, Variance, StdDev

    @unittest.skipUnless(connection.vendor == 'sqlite',

                         "No need to do SQLite checks")

    def test_convert_values_to_handle_null_value(self):

        from django.db.backends.sqlite3.base import DatabaseOperations

        database_operations = DatabaseOperations(connection)

        self.assertEqual(

            None,

        a = ["ᄲawef"]

        b = self.select(a)

        self.assertEqual(a[0], b[0])

@unittest.skipUnless(

    connection.vendor == 'postgresql',

    "This test applies only to PostgreSQL")

class PostgresLookupCastTests(TestCase):

    def test_lookup_cast(self):

        from django.db.backends.postgresql_psycopg2.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))