Fixing testing

ethereumj-core/src/test/java/org/ethereum/core/BlockTest.java

@@ -162,6 +162,7 @@ public class BlockTest {
     
     @Test
     public void testCalcDifficulty() {
+        try {
             Block genesis = Genesis.getInstance();
             BigInteger difficulty = new BigInteger(1, genesis.calcDifficulty());
             System.out.println("Genesis difficulty = " + difficulty.toString());
@@ -177,6 +178,9 @@ public class BlockTest {
             System.out.println("Block#1 actual difficulty = " + actualDifficulty.toString());
             System.out.println("Block#1 calculated difficulty = " + calcDifficulty.toString());
             assertEquals(actualDifficulty, calcDifficulty);
+        } finally {
+            WorldManager.instance.close();
+        }
     }
     
     @Test