assertNumQueries should ignore initial connection configuration queries

[François Freitag]

Upon connection to the database, Django may trigger queries to configure the connection state (e.g. ​MySQL transaction isolation and AUTO_IS_NULL, ​oracle dates format, ​postgresql timezones).
IMHO, these queries should be ignored by assertNumQueries.

My use case, on MySQL 5.5.54-0 and MariaDB 10.1.23-1:

from django.contrib.contenttypes.models import ContentType
from django.test import TransactionTestCase


class MyTests(TransactionTestCase):

    available_apps = []

    def test_assertNumQueries_counts_db_configuration_queries(self):
        # Emulates connection being closed after previous query/test
        # possibly because the connection expired (e.g. CONN_MAX_AGE=0)
        connection.close()  
        
        with self.assertNumQueries(1):
            list(ContentType.objects.all())

        # Fails with:
        # AssertionError: 2 != 1 : 2 queries executed, 1 expected
        # Captured queries were:
        # SET TX_ISOLATION = 'read-committed'
        # SELECT `django_content_type`.`id`, `django_content_type`.`app_label`, `django_content_type`.`model` FROM `django_content_type`

Thanks to Cole Maclean for the initial report.

[François Freitag]

​PR

[Tim Graham <timograham@…>]

In 98b3b14a:

Fixed #28203 -- Ignored connection configuration queries in assertNumQueries().