Index: src/test/org/apache/lucene/index/TestNRTReaderWithThreads.java
===================================================================
--- src/test/org/apache/lucene/index/TestNRTReaderWithThreads.java	(revision 912337)
+++ src/test/org/apache/lucene/index/TestNRTReaderWithThreads.java	(working copy)
@@ -54,13 +54,16 @@
     int addCount = 0;
     for (int x=0; x < indexThreads.length; x++) {
       indexThreads[x].run = false;
-      assertTrue(indexThreads[x].ex == null);
+      assertNull("Exception thrown: "+indexThreads[x].ex, indexThreads[x].ex);
       addCount += indexThreads[x].addCount;
       delCount += indexThreads[x].delCount;
     }
     for (int x=0; x < indexThreads.length; x++) {
       indexThreads[x].join();
     }
+    for (int x=0; x < indexThreads.length; x++) {
+      assertNull("Exception thrown: "+indexThreads[x].ex, indexThreads[x].ex);
+    }
     //System.out.println("addCount:"+addCount);
     //System.out.println("delCount:"+delCount);
     writer.close();
@@ -69,8 +72,8 @@
 
   public class RunThread extends Thread {
     IndexWriter writer;
-    boolean run = true;
-    Throwable ex;
+    volatile boolean run = true;
+    volatile Throwable ex;
     int delCount = 0;
     int addCount = 0;
     int type;
Index: src/test/org/apache/lucene/util/LuceneTestCase.java
===================================================================
--- src/test/org/apache/lucene/util/LuceneTestCase.java	(revision 912337)
+++ src/test/org/apache/lucene/util/LuceneTestCase.java	(working copy)
@@ -21,6 +21,9 @@
 import java.util.Arrays;
 import java.util.Iterator;
 import java.util.Random;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Collections;
 
 import junit.framework.TestCase;
 
@@ -57,6 +60,19 @@
   public static final Version TEST_VERSION_CURRENT = LuceneTestCaseJ4.TEST_VERSION_CURRENT;
 
   private int savedBoolMaxClauseCount;
+  
+  private volatile Thread.UncaughtExceptionHandler savedUncaughtExceptionHandler = null;
+  
+  private static class UncaughtExceptionEntry {
+    public final Thread thread;
+    public final Throwable exception;
+    
+    public UncaughtExceptionEntry(Thread thread, Throwable exception) {
+      this.thread = thread;
+      this.exception = exception;
+    }
+  }
+  private List<UncaughtExceptionEntry> uncaughtExceptions = Collections.synchronizedList(new ArrayList<UncaughtExceptionEntry>());
 
   public LuceneTestCase() {
     super();
@@ -69,6 +85,16 @@
   @Override
   protected void setUp() throws Exception {
     super.setUp();
+    
+    savedUncaughtExceptionHandler = Thread.getDefaultUncaughtExceptionHandler();
+    Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
+      public void uncaughtException(Thread t, Throwable e) {
+        uncaughtExceptions.add(new UncaughtExceptionEntry(t, e));
+        if (savedUncaughtExceptionHandler != null)
+          savedUncaughtExceptionHandler.uncaughtException(t, e);
+      }
+    });
+    
     ConcurrentMergeScheduler.setTestMode();
     savedBoolMaxClauseCount = BooleanQuery.getMaxClauseCount();
   }
@@ -111,6 +137,16 @@
       purgeFieldCache(FieldCache.DEFAULT);
     }
     
+    Thread.setDefaultUncaughtExceptionHandler(savedUncaughtExceptionHandler);
+    if (!uncaughtExceptions.isEmpty()) {
+      System.err.println("The following exceptions were thrown by threads:");
+      for (UncaughtExceptionEntry entry : uncaughtExceptions) {
+        System.err.println("*** Thread: " + entry.thread.getName() + " ***");
+        entry.exception.printStackTrace(System.err);
+      }
+      fail("Some threads throwed uncaught exceptions!");
+    }
+    
     super.tearDown();
   }
 
Index: src/test/org/apache/lucene/util/LuceneTestCaseJ4.java
===================================================================
--- src/test/org/apache/lucene/util/LuceneTestCaseJ4.java	(revision 912337)
+++ src/test/org/apache/lucene/util/LuceneTestCaseJ4.java	(working copy)
@@ -31,6 +31,9 @@
 import java.util.Arrays;
 import java.util.Iterator;
 import java.util.Random;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Collections;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.fail;
@@ -79,6 +82,19 @@
 
   private int savedBoolMaxClauseCount;
 
+  private volatile Thread.UncaughtExceptionHandler savedUncaughtExceptionHandler = null;
+  
+  private static class UncaughtExceptionEntry {
+    public final Thread thread;
+    public final Throwable exception;
+    
+    public UncaughtExceptionEntry(Thread thread, Throwable exception) {
+      this.thread = thread;
+      this.exception = exception;
+    }
+  }
+  private List<UncaughtExceptionEntry> uncaughtExceptions = Collections.synchronizedList(new ArrayList<UncaughtExceptionEntry>());
+
   // This is how we get control when errors occur.
   // Think of this as start/end/success/failed
   // events.
@@ -94,6 +110,15 @@
 
   @Before
   public void setUp() throws Exception {
+    savedUncaughtExceptionHandler = Thread.getDefaultUncaughtExceptionHandler();
+    Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
+      public void uncaughtException(Thread t, Throwable e) {
+        uncaughtExceptions.add(new UncaughtExceptionEntry(t, e));
+        if (savedUncaughtExceptionHandler != null)
+          savedUncaughtExceptionHandler.uncaughtException(t, e);
+      }
+    });
+    
     ConcurrentMergeScheduler.setTestMode();
     savedBoolMaxClauseCount = BooleanQuery.getMaxClauseCount();
     seed = null;
@@ -138,6 +163,16 @@
     } finally {
       purgeFieldCache(FieldCache.DEFAULT);
     }
+    
+    Thread.setDefaultUncaughtExceptionHandler(savedUncaughtExceptionHandler);
+    if (!uncaughtExceptions.isEmpty()) {
+      System.err.println("The following exceptions were thrown by threads:");
+      for (UncaughtExceptionEntry entry : uncaughtExceptions) {
+        System.err.println("*** Thread: " + entry.thread.getName() + " ***");
+        entry.exception.printStackTrace(System.err);
+      }
+      fail("Some threads throwed uncaught exceptions!");
+    }
   }
 
   /**