diff --git a/02_hash_maps/hm_test.py b/02_hash_maps/hm_test.py
index 3e8b909..985a78e 100644
--- a/02_hash_maps/hm_test.py
+++ b/02_hash_maps/hm_test.py
@@ -12,15 +12,37 @@ import unittest
 
 class test_hash_map_neighbour_collision(unittest.TestCase):
 
-	def test_add(self):
+	def test__find_free_idx(self):
 		hm = HMNeighbourCollision()
 		
-		hm.add("One", "Ibiza")
+		key = "One"
+		value = "Ibiza"
+		
+		my_key = hm._hash(key)
+		idx = hm._find_free_idx(my_key)
+		self.assertEqual(my_key, idx)
+		
+		hm.add(key, value)
 		self.assertEqual(hm.size(), 1)
 		
-		hm.add("One", "Ibiza2")
+		# We move one up
+		idx = hm._find_free_idx(my_key)		
+		self.assertEqual(my_key - 1, idx)
+		
+		hm.add(key, "Ibiza2")
 		self.assertEqual(hm.size(), 2)	
 
+		# We move one down
+		idx = hm._find_free_idx(my_key)		
+		self.assertEqual(my_key + 1, idx)
+
+		hm.add(key, "Ibiza3")
+		self.assertEqual(hm.size(), 3)	
+
+		# We move two up
+		idx = hm._find_free_idx(my_key)		
+		self.assertEqual(my_key - 2, idx)
+
 class test_hash_map_table_collision(unittest.TestCase):
 
 	def test_add(self):