Fix broken unit test

src/test/java/com/zaxxer/hikari/CreationTest.java

@@ -221,9 +221,11 @@ public class CreationTest
     public void testIsolation() throws Exception
     {
         HikariConfig config = new HikariConfig();
+        config.setDataSourceClassName("com.zaxxer.hikari.mocks.StubDataSource");
         config.setTransactionIsolation("TRANSACTION_REPEATABLE_READ");
+        config.validate();
+        
         int transactionIsolation = config.getTransactionIsolation();
-
         Assert.assertSame(Connection.TRANSACTION_REPEATABLE_READ, transactionIsolation);
     }
 }