Fixes reverse rank calculation

bookwyrm/suggested_users.py

@@ -24,7 +24,7 @@ class SuggestedUsers(RedisStore):
         """calculate mutuals count and shared books count from rank"""
         return {
             "mutuals": math.floor(rank),
-            "shared_books": int(1 / (-1 * (1 % rank - 1))) if rank else 0,
+            "shared_books": int(1 / (-1 * (rank % 1 - 1))) - 1,
         }
 
     def get_objects_for_store(self, store):

bookwyrm/tests/test_suggested_users.py

@@ -0,0 +1,69 @@
+""" testing user follow suggestions """
+from collections import namedtuple
+from unittest.mock import patch
+
+from django.test import TestCase
+
+from bookwyrm import models
+from bookwyrm.suggested_users import suggested_users
+
+
+@patch("bookwyrm.models.activitypub_mixin.broadcast_task.delay")
+@patch("bookwyrm.activitystreams.ActivityStream.add_status")
+class SuggestedUsers(TestCase):
+    """using redis to build activity streams"""
+
+    def setUp(self):
+        """use a test csv"""
+        self.local_user = models.User.objects.create_user(
+            "mouse", "mouse@mouse.mouse", "password", local=True, localname="mouse"
+        )
+        self.book = models.Edition.objects.create(title="test book")
+
+    def test_get_ramk(self, *_):
+        """a float that reflects both the mutuals count and shared books"""
+        Mock = namedtuple("AnnotatedUserMock", ("mutuals", "shared_books"))
+        annotated_user_mock = Mock(3, 27)
+        rank = suggested_users.get_rank(annotated_user_mock)
+        self.assertEqual(rank, 3.9642857142857144)
+
+    def test_store_id(self, *_):
+        """redis key generation"""
+        self.assertEqual(
+            suggested_users.store_id(self.local_user),
+            "{:d}-suggestions".format(self.local_user.id),
+        )
+
+    def test_get_counts_from_rank(self, *_):
+        """reverse the rank computation to get the mutuals and shared books counts"""
+        counts = suggested_users.get_counts_from_rank(3.9642857142857144)
+        self.assertEqual(counts["mutuals"], 3)
+        self.assertEqual(counts["shared_books"], 27)
+
+    def test_get_objects_for_store(self, *_):
+        """list of people to follow for a given user"""
+
+        mutual_user = models.User.objects.create_user(
+            "rat", "rat@local.rat", "password", local=True, localname="rat"
+        )
+        suggestable_user = models.User.objects.create_user(
+            "nutria",
+            "nutria@nutria.nutria",
+            "password",
+            local=True,
+            localname="nutria",
+            discoverable=True,
+        )
+
+        # you follow rat
+        mutual_user.followers.add(self.local_user)
+        # rat follows the suggested user
+        suggestable_user.followers.add(mutual_user)
+
+        results = suggested_users.get_objects_for_store(
+            "{:d}-suggestions".format(self.local_user.id)
+        )
+        self.assertEqual(results.count(), 1)
+        match = results.first()
+        self.assertEqual(match.id, suggestable_user.id)
+        self.assertEqual(match.mutuals, 1)