diff --git a/src/postings/docset.rs b/src/postings/docset.rs
index 1f182586e..63cf24067 100644
--- a/src/postings/docset.rs
+++ b/src/postings/docset.rs
@@ -2,6 +2,7 @@ use DocId;
 use std::borrow::Borrow;
 use std::borrow::BorrowMut;
 use std::cmp::Ordering;
+use std::iter::Iterator;
 
 #[derive(PartialEq, Eq, Debug)]
 pub enum SkipResult {
@@ -34,6 +35,15 @@ pub trait DocSet {
     }
 
     fn doc(&self,) -> DocId;
+    
+    fn next(&mut self) -> Option<DocId> {
+        if self.advance() {
+            Some(self.doc())
+        }
+        else {
+            None
+        }
+    }
 }
 
 
diff --git a/src/postings/union_postings.rs b/src/postings/union_postings.rs
index 876532f95..27b9e49bb 100644
--- a/src/postings/union_postings.rs
+++ b/src/postings/union_postings.rs
@@ -170,17 +170,13 @@ mod tests {
             vec!(left, right),
             multi_term_scorer
         );
-        assert!(union.advance());
-        assert_eq!(union.doc(), 1);
+        assert_eq!(union.next(), Some(1u32));
         assert!(abs_diff(union.scorer().score(), 2.182179f32) < 0.001);
-        assert!(union.advance());
-        assert_eq!(union.doc(), 2);
+        assert_eq!(union.next(), Some(2u32));
         assert!(abs_diff(union.scorer().score(), 0.2236068) < 0.001f32);
-        assert!(union.advance());
-        assert_eq!(union.doc(), 3);
-        assert!(union.advance());
+        assert_eq!(union.next(), Some(3u32));
+        assert_eq!(union.next(), Some(8u32));
         assert!(abs_diff(union.scorer().score(), 0.8944272f32) < 0.001f32);
-        assert_eq!(union.doc(), 8);
         assert!(!union.advance());
     }