diff --git a/src/indexer/index_writer.rs b/src/indexer/index_writer.rs
index 28c428924..0fbb9913c 100644
--- a/src/indexer/index_writer.rs
+++ b/src/indexer/index_writer.rs
@@ -359,7 +359,11 @@ impl IndexWriter {
             .add_segment(self.generation, segment_entry);
     }
 
-    #[doc(hidden)]
+    /// *Experimental & Advanced API* Creates a new segment.
+    /// and marks it as currently in write.
+    ///
+    /// This method is useful only for users trying to do complex
+    /// operations, like converting an index format to another.
     pub fn new_segment(&self) -> Segment {
         self.segment_updater.new_segment()
     }
diff --git a/src/query/vec_docset.rs b/src/query/vec_docset.rs
index 1aa07861c..01ca081be 100644
--- a/src/query/vec_docset.rs
+++ b/src/query/vec_docset.rs
@@ -69,4 +69,20 @@ pub mod tests {
         assert_eq!(postings.skip_next(6000u32), SkipResult::End);
     }
 
+    #[test]
+    pub fn test_fill_buffer() {
+        let doc_ids: Vec<DocId> = (1u32..210u32).collect();
+        let mut postings = VecDocSet::from(doc_ids);
+        let mut buffer = vec![1000u32; 100];
+        assert_eq!(postings.fill_buffer(&mut buffer[..]), 100);
+        for i in 0u32..100u32 {
+            assert_eq!(buffer[i as usize], i + 1);
+        }
+        assert_eq!(postings.fill_buffer(&mut buffer[..]), 100);
+        for i in 0u32..100u32 {
+            assert_eq!(buffer[i as usize], i + 101);
+        }
+        assert_eq!(postings.fill_buffer(&mut buffer[..]), 9);
+    }
+
 }