Index: lucene/src/test/org/apache/lucene/index/TestTermVectorsReader.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/TestTermVectorsReader.java	(revision 988752)
+++ lucene/src/test/org/apache/lucene/index/TestTermVectorsReader.java	(working copy)
@@ -394,6 +394,8 @@
       fail();
     } catch (IOException e) {
       // expected exception
+    } catch (IllegalArgumentException e) {
+      // mmapdir will give us this from java.nio.Buffer.position()
     } finally {
       reader.close();
     }
@@ -404,6 +406,8 @@
       fail();
     } catch (IOException e) {
       // expected exception
+    } catch (IllegalArgumentException e) {
+      // mmapdir will give us this from java.nio.Buffer.position()
     } finally {
       reader.close();
     }
Index: lucene/src/test/org/apache/lucene/index/TestIndexWriter.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/TestIndexWriter.java	(revision 988752)
+++ lucene/src/test/org/apache/lucene/index/TestIndexWriter.java	(working copy)
@@ -4377,10 +4377,8 @@
 
     @Override
     public void run() {
-      Directory dir;
-      try { 
-        dir = newDirectory(random); 
-      } catch (IOException e) { throw new RuntimeException(e); }
+      // LUCENE-2239: won't work with NIOFS/MMAP
+      Directory dir = new MockDirectoryWrapper(new RAMDirectory()); 
       IndexWriter w = null;
       while(!finish) {
         try {
Index: lucene/src/test/org/apache/lucene/util/LuceneTestCaseJ4.java
===================================================================
--- lucene/src/test/org/apache/lucene/util/LuceneTestCaseJ4.java	(revision 988752)
+++ lucene/src/test/org/apache/lucene/util/LuceneTestCaseJ4.java	(working copy)
@@ -27,6 +27,7 @@
 import org.apache.lucene.search.FieldCache;
 import org.apache.lucene.search.FieldCache.CacheEntry;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.MMapDirectory;
 import org.apache.lucene.store.MockDirectoryWrapper;
 import org.apache.lucene.store.RAMDirectory;
 import org.apache.lucene.util.FieldCacheSanityChecker.Insanity;
@@ -642,7 +643,11 @@
         tmpFile.mkdir();
         try {
           Constructor<? extends Directory> ctor = clazz.getConstructor(File.class);
-          return ctor.newInstance(tmpFile);
+          Directory d = ctor.newInstance(tmpFile);
+          // try not to enable this hack unless we must.
+          if (d instanceof MMapDirectory && Constants.WINDOWS && MMapDirectory.UNMAP_SUPPORTED)
+            ((MMapDirectory)d).setUseUnmap(true);
+          return d;
         } catch (Exception e2) {
           // try .open(File)
           Method method = clazz.getMethod("open", new Class[] { File.class });