Set the serialized_aliases argument of setup_databases.

pytest_django/fixtures.py

@@ -144,6 +144,7 @@ def django_db_setup(
         db_cfg = setup_databases(
             verbosity=request.config.option.verbose,
             interactive=False,
+            serialized_aliases=_get_serialized_aliases(request.session.items),
             **setup_databases_args,
         )
 
@@ -301,6 +302,34 @@ def handle(self, *args, **kwargs):
     migrate.Command = MigrateSilentCommand
 
 
+def _get_serialized_aliases(tests: list) -> set:
+    """
+    Get a set of `serialized_aliases` to be used with `setup_databases`.
+
+    The `serialized_aliases` argument of the `setup_databases` function determines what subset of aliases test
+    databases should have their state serialized to allow usage of the `serialized_rollback` feature. If it's not
+    provided, it defaults to aliases.
+
+    Django 5 removed the `SERIALIZE` test setting, as it can be inferred from the databases with the
+    `serialized_rollback` option enabled. Django's default test runner, `DiscoverRunner`, uses logic similar to this to
+    build the `serialized_aliases` set and pass it to `setup_databases`, as implemented in
+    `django.test.runner.DiscoverRunner.run_tests`.
+    """
+    from django.db import connections
+
+    databases = {}
+    for test in tests:
+        if not (marker := test.get_closest_marker("django_db")):
+            continue
+        (_, _, test_databases, serialized_rollback, _) = validate_django_db(marker)
+        if test_databases == "__all__":
+            test_databases = connections
+        if test_databases:
+            databases.update((alias, serialized_rollback or databases.get(alias, False)) for alias in test_databases)
+    serialized_aliases = {alias for alias, serialize in databases.items() if serialize}
+    return serialized_aliases
+
+
 def _set_suffix_to_test_databases(suffix: str) -> None:
     from django.conf import settings