Fix state tests a little

tests/migrations/test_state.py

@@ -1,7 +1,7 @@
 from django.test import TestCase
 from django.db import models
 from django.db.models.loading import BaseAppCache
-from django.db.migrations.state import ProjectState
+from django.db.migrations.state import ProjectState, ModelState
 
 
 class StateTests(TestCase):
@@ -13,6 +13,7 @@ class StateTests(TestCase):
         """
         Tests making a ProjectState from an AppCache
         """
+
         new_app_cache = BaseAppCache()
 
         class Author(models.Model):
@@ -41,3 +42,31 @@ class StateTests(TestCase):
         self.assertEqual(author_state.fields[2][1].null, False)
         self.assertEqual(author_state.fields[3][1].null, True)
         self.assertEqual(author_state.bases, (models.Model, ))
+        
+        self.assertEqual(book_state.app_label, "migrations")
+        self.assertEqual(book_state.name, "Book")
+        self.assertEqual([x for x, y in book_state.fields], ["id", "title", "author"])
+        self.assertEqual(book_state.fields[1][1].max_length, 1000)
+        self.assertEqual(book_state.fields[2][1].null, False)
+        self.assertEqual(book_state.bases, (models.Model, ))
+
+    def test_render(self):
+        """
+        Tests rendering a ProjectState into an AppCache.
+        """
+        project_state = ProjectState()
+        project_state.add_model_state(ModelState(
+            "migrations",
+            "Tag",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=100)),
+                ("hidden", models.BooleanField()),
+            ],
+            {},
+            None,
+        ))
+
+        new_app_cache = project_state.render()
+        self.assertEqual(new_app_cache.get_model("migrations", "Tag")._meta.get_field_by_name("name")[0].max_length, 100)
+        self.assertEqual(new_app_cache.get_model("migrations", "Tag")._meta.get_field_by_name("hidden")[0].null, False)