Test that the lucene "unmap hack" is supported.

We should know if this is not working for any configuration, otherwise resources such as address space, file handles, and even disk space become tied to Java's garbage collector.

Author: rmuir

core/src/test/java/org/elasticsearch/common/lucene/LuceneTests.java

@@ -28,6 +28,7 @@
 import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.MMapDirectory;
 import org.apache.lucene.store.MockDirectoryWrapper;
 import org.apache.lucene.util.Version;
 import org.elasticsearch.test.ESTestCase;
@@ -359,4 +360,15 @@ public void testCount() throws Exception {
         w.close();
         dir.close();
     }
+
+    /**
+     * Test that the "unmap hack" is detected as supported by lucene.
+     * <p>
+     * While not guaranteed, current status is "Critical Internal API": http://openjdk.java.net/jeps/260
+     * Additionally this checks we did not screw up the security logic around the hack.
+     */
+    public void testMMapHackSupported() throws Exception {
+        // add assume's here if needed for certain platforms, but we should know if it does not work.
+        assertTrue(MMapDirectory.UNMAP_SUPPORTED);
+    }
 }