Add a test for connection.database in the connection_created signal.

I contemplated removing the self.database assignment from
DatabaseWrapper.init_connection_state() which would have broken this.

Author: timgraham

tests/backend_/test_base.py

@@ -1,5 +1,6 @@
 from django.core.exceptions import ImproperlyConfigured
 from django.db import connection
+from django.db.backends.signals import connection_created
 from django.test import SimpleTestCase, TestCase
 
 from django_mongodb_backend.base import DatabaseWrapper
@@ -21,3 +22,23 @@ def test_set_autocommit(self):
         self.assertIs(connection.get_autocommit(), False)
         connection.set_autocommit(True)
         self.assertIs(connection.get_autocommit(), True)
+
+    def test_connection_created_database_attr(self):
+        """
+        connection.database is available in the connection_created signal.
+        """
+        data = {}
+
+        def receiver(sender, connection, **kwargs):  # noqa: ARG001
+            data["database"] = connection.database
+
+        connection_created.connect(receiver)
+        connection.close()
+        # Accessing database implicitly connects.
+        connection.database  # noqa: B018
+        self.assertIs(data["database"], connection.database)
+        connection.close()
+        connection_created.disconnect(receiver)
+        data.clear()
+        connection.connect()
+        self.assertEqual(data, {})