assert every point's friends queue has correct max size

pkg/hnsw/hnsw.go

@@ -213,16 +213,13 @@ func (h *Hnsw) InsertVector(q Point) error {
 		// add bidirectional connections from neighbors to q at layer c
 		for _, neighbor := range neighbors {
 			neighborPoint := h.points[neighbor.id]
-
 			distNeighToQ := EuclidDistance(*neighborPoint, q)
-
 			h.friends[neighbor.id].InsertFriendsAtLevel(level, qId, distNeighToQ)
 			h.friends[qId].InsertFriendsAtLevel(level, neighbor.id, distNeighToQ)
 		}
 
 		for _, neighbor := range neighbors {
 			neighborFriendsAtLevel, err := h.friends[neighbor.id].GetFriendsAtLevel(level)
-
 			if err != nil {
 				return fmt.Errorf("failed to find nearest neighbor to Q at level %v: %w", level, err)
 			}

pkg/hnsw/hnsw_test.go

@@ -436,7 +436,7 @@ func TestHnsw_InsertVector(t *testing.T) {
 	t.Run("bulk insert", func(t *testing.T) {
 		items := 1
 
-		h := NewHnsw(3, 4, 4, Point{0, 0, 0})
+		h := NewHnsw(3, 4, 10, Point{0, 0, 0})
 
 		for i := 100; i >= 1; i-- {
 			j := float32(i)
@@ -465,6 +465,34 @@ func TestHnsw_InsertVector(t *testing.T) {
 
 			items += 1
 		}
+
+		// ensure every friend pq is of max length 4
+		var allNodeIds []Id
+		for id := range h.friends {
+			allNodeIds = append(allNodeIds, id)
+		}
+
+		for _, nodeId := range allNodeIds {
+			nodeFriends, ok := h.friends[nodeId]
+			if !ok {
+				t.Fatalf("expected to find point for node %v", nodeId)
+			}
+
+			for level, friendsAtLevel := range nodeFriends.friends {
+				if level == 0 {
+					if friendsAtLevel.Len() > h.Mmax0 {
+						t.Fatalf("node id %v, num friends at level 0 cannot be greater than max number of connections M = %v. Got %v", nodeId, h.M, friendsAtLevel.Len())
+					}
+
+					continue
+				}
+
+				if friendsAtLevel.Len() > h.M {
+					t.Fatalf("num friends at level %v cannot be greater than max number of connections M: %v. Got: %v", level, h.M, friendsAtLevel.Len())
+				}
+			}
+
+		}
 	})
 
 	t.Run("basic cluster insertion", func(t *testing.T) {