Created a new tests folder (model_options).

And moved `tablespaces` option tests to it.
The new folder can be used to test models/options, like the new option
added in refs #22778.

tests/model_options/models/tablespaces.py

@@ -0,0 +1,48 @@
+from django.db import models
+
+# Since the test database doesn't have tablespaces, it's impossible for Django
+# to create the tables for models where db_tablespace is set. To avoid this
+# problem, we mark the models as unmanaged, and temporarily revert them to
+# managed during each test. We also set them to use the same tables as the
+# "reference" models to avoid errors when other tests run 'migrate'
+# (proxy_models_inheritance does).
+
+
+class ScientistRef(models.Model):
+    name = models.CharField(max_length=50)
+
+
+class ArticleRef(models.Model):
+    title = models.CharField(max_length=50, unique=True)
+    code = models.CharField(max_length=50, unique=True)
+    authors = models.ManyToManyField(ScientistRef, related_name='articles_written_set')
+    reviewers = models.ManyToManyField(ScientistRef, related_name='articles_reviewed_set')
+
+
+class Scientist(models.Model):
+    name = models.CharField(max_length=50)
+
+    class Meta:
+        db_table = 'model_options_scientistref'
+        db_tablespace = 'tbl_tbsp'
+        managed = False
+
+
+class Article(models.Model):
+    title = models.CharField(max_length=50, unique=True)
+    code = models.CharField(max_length=50, unique=True, db_tablespace='idx_tbsp')
+    authors = models.ManyToManyField(Scientist, related_name='articles_written_set')
+    reviewers = models.ManyToManyField(Scientist, related_name='articles_reviewed_set', db_tablespace='idx_tbsp')
+
+    class Meta:
+        db_table = 'model_options_articleref'
+        db_tablespace = 'tbl_tbsp'
+        managed = False
+
+# Also set the tables for automatically created models
+
+Authors = Article._meta.get_field('authors').rel.through
+Authors._meta.db_table = 'model_options_articleref_authors'
+
+Reviewers = Article._meta.get_field('reviewers').rel.through
+Reviewers._meta.db_table = 'model_options_articleref_reviewers'