get_next_story_part: implement & test

stories/writingtogether/models.py

@@ -17,8 +17,11 @@ class StoryRound(models.Model):
         return reverse('writing:detail', kwargs={'pk': self.pk})
 
     def get_next_story_part(self, user: User) -> 'StoryPart':
-        # TODO: implement, for each story get unfinished part and check user
-        pass
+        return StoryPart.objects.get(
+            part_of__part_of_round=self,
+            turn_number=self.current_turn,
+            user=user
+        )
 
     def next_round_ready(self) -> bool:
         for story in self.story_set.all():

stories/writingtogether/tests/test_model_functions.py

@@ -117,3 +117,29 @@ class TestModelFunctions(TestCase):
         self.parts2[1].text = 'some text'
         self.parts2[1].save()
         self.assertTrue(self.story_round.next_round_ready())
+
+    def test_get_next_story_part__each_user_starts_with_own_story(self):
+        self.create_users_and_story_round_with_stories_and_parts()
+
+        result = self.story_round.get_next_story_part(self.user1)
+        self.assertEqual(result, self.parts1[0])
+
+        result = self.story_round.get_next_story_part(self.user2)
+        self.assertEqual(result, self.parts2[0])
+
+    def test_get_next_story_part__second_round_story_switched(self):
+        self.create_users_and_story_round_with_stories_and_parts()
+        self.parts1[0].text = 'some text'
+        self.parts1[0].save()
+
+        self.parts2[0].text = 'some text'
+        self.parts2[0].save()
+
+        self.story_round.current_turn = 1
+        self.story_round.save()
+
+        result = self.story_round.get_next_story_part(self.user1)
+        self.assertEqual(result, self.parts2[1])
+
+        result = self.story_round.get_next_story_part(self.user2)
+        self.assertEqual(result, self.parts1[1])