Filtered out 'base' from database backend choices error message.

        try:

            builtin_backends = [

                name for _, name, ispkg in pkgutil.iter_modules([backend_dir])

                if ispkg and name != 'dummy']

                if ispkg and name not in {'base', 'dummy'}]

        except EnvironmentError:

            builtin_backends = []

        if backend_name not in ['django.db.backends.%s' % b for b in

from django.core.exceptions import ImproperlyConfigured

from django.db.utils import load_backend

from django.test import SimpleTestCase

from django.test.utils import str_prefix

from django.utils import six

class TestLoadBackend(SimpleTestCase):

    def test_load_backend_invalid_name(self):

        msg = str_prefix(

            "'foo' isn't an available database backend.\n"

            "Try using 'django.db.backends.XXX', where XXX is one of:\n"

            "    %(_)s'mysql', %(_)s'oracle', %(_)s'postgresql_psycopg2', %(_)s'sqlite3'\n"

            "Error was: No module named %%s"

        ) % "foo.base" if six.PY2 else "'foo'"

        with self.assertRaisesMessage(ImproperlyConfigured, msg):

            load_backend('foo')