Index: lucene/core/src/test/org/apache/lucene/search/payloads/TestPayloadNearQuery.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/search/payloads/TestPayloadNearQuery.java	(revision 1397735)
+++ lucene/core/src/test/org/apache/lucene/search/payloads/TestPayloadNearQuery.java	(working copy)
@@ -341,6 +341,7 @@
     // idf used for phrase queries
     @Override 
     public Explanation idfExplain(CollectionStatistics collectionStats, TermStatistics[] termStats) {
+      wasCalled = true;
       return new Explanation(1.0f, "Inexplicable");
     }
   }
Index: lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java	(revision 1397735)
+++ lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java	(working copy)
@@ -108,6 +108,9 @@
  * @lucene.experimental
  */
 public abstract class Similarity {
+
+  // nocommit
+  public boolean wasCalled;
   
   /**
    * Sole constructor. (For invocation by subclass 
Index: lucene/core/src/java/org/apache/lucene/search/similarities/DefaultSimilarity.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/search/similarities/DefaultSimilarity.java	(revision 1397735)
+++ lucene/core/src/java/org/apache/lucene/search/similarities/DefaultSimilarity.java	(working copy)
@@ -106,8 +106,12 @@
     return discountOverlaps;
   }
 
+  // nocommit
+
+  /*
   @Override
   public String toString() {
     return "DefaultSimilarity";
   }
+  */
 }
Index: lucene/core/src/java/org/apache/lucene/search/similarities/TFIDFSimilarity.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/search/similarities/TFIDFSimilarity.java	(revision 1397735)
+++ lucene/core/src/java/org/apache/lucene/search/similarities/TFIDFSimilarity.java	(working copy)
@@ -730,9 +730,17 @@
 
   @Override
   public final SimWeight computeWeight(float queryBoost, CollectionStatistics collectionStats, TermStatistics... termStats) {
+    wasCalled = false;
     final Explanation idf = termStats.length == 1
     ? idfExplain(collectionStats, termStats[0])
     : idfExplain(collectionStats, termStats);
+    if (toString().indexOf("TestPayloadNearQuery$BoostingSimilarity@") != -1) {
+      if (!wasCalled) {
+        System.out.println("FAILED");
+        throw new RuntimeException("overridden idfExplain method in TestPayloadNearQuery.BoostingSimilarity was not called");
+      }
+    }
+
     return new IDFStats(collectionStats.field(), idf, queryBoost);
   }
 
Index: lucene/core/src/java/org/apache/lucene/util/fst/Util.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/util/fst/Util.java	(revision 1397735)
+++ lucene/core/src/java/org/apache/lucene/util/fst/Util.java	(working copy)
@@ -400,6 +400,7 @@
           continue;
         }
 
+        // nocommit this isn't safe?  last path could be rejected?
         if (results.size() == topN-1) {
           // Last path -- don't bother w/ queue anymore:
           queue = null;