diff --git a/python/gtsam/tests/test_dsf_map.py b/python/gtsam/tests/test_dsf_map.py
index e36657178..0ab8b678f 100644
--- a/python/gtsam/tests/test_dsf_map.py
+++ b/python/gtsam/tests/test_dsf_map.py
@@ -6,49 +6,68 @@ All Rights Reserved
 See LICENSE for the license information
 
 Unit tests for Disjoint Set Forest.
-Author: Frank Dellaert & Varun Agrawal
+Author: Frank Dellaert & Varun Agrawal & John Lambert
 """
 # pylint: disable=invalid-name, no-name-in-module, no-member
 
 from __future__ import print_function
 
 import unittest
+from typing import Tuple
 
 import gtsam
+from gtsam import IndexPair
 from gtsam.utils.test_case import GtsamTestCase
 
 
 class TestDSFMap(GtsamTestCase):
     """Tests for DSFMap."""
 
-    def test_all(self):
+    def test_all(self) -> None:
         """Test everything in DFSMap."""
-        def key(index_pair):
+
+        def key(index_pair) -> Tuple[int, int]:
             return index_pair.i(), index_pair.j()
 
         dsf = gtsam.DSFMapIndexPair()
         pair1 = gtsam.IndexPair(1, 18)
         self.assertEqual(key(dsf.find(pair1)), key(pair1))
         pair2 = gtsam.IndexPair(2, 2)
-        
+
         # testing the merge feature of dsf
         dsf.merge(pair1, pair2)
         self.assertEqual(key(dsf.find(pair1)), key(dsf.find(pair2)))
 
-    def test_sets(self):
-        from gtsam import IndexPair
+    def test_sets(self) -> None:
+        """Ensure that unique keys are merged correctly during Union-Find.
+
+        An IndexPair (i,k) representing a unique key might represent the
+        k'th detected keypoint in image i. For the data below, merging such
+        measurements into feature tracks across frames should create 2 distinct sets.
+        """
         dsf = gtsam.DSFMapIndexPair()
-        dsf.merge(IndexPair(0, 1), IndexPair(1,2))
-        dsf.merge(IndexPair(0, 1), IndexPair(3,4))
-        dsf.merge(IndexPair(4,5), IndexPair(6,8))
+        dsf.merge(IndexPair(0, 1), IndexPair(1, 2))
+        dsf.merge(IndexPair(0, 1), IndexPair(3, 4))
+        dsf.merge(IndexPair(4, 5), IndexPair(6, 8))
         sets = dsf.sets()
 
+        merged_sets = set()
+
         for i in sets:
+            set_keys = []
             s = sets[i]
             for val in gtsam.IndexPairSetAsArray(s):
-                val.i()
-                val.j()
+                set_keys.append((val.i(), val.j()))
+            merged_sets.add(tuple(set_keys))
+
+        # fmt: off
+        expected_sets = {
+            ((0, 1), (1, 2), (3, 4)), # set 1
+            ((4, 5), (6, 8)) # set 2
+        }
+        # fmt: on
+        assert expected_sets == merged_sets
 
 
-if __name__ == '__main__':
+if __name__ == "__main__":
     unittest.main()