@Test
    public void createIndexErrorMessage() throws Exception {
        final MongoClient client = new MongoClient();
        try {
            final DBCollection collection = client.getDB("test").getCollection("foo");
            collection.drop();
            collection.insert(new BasicDBObject("a", 1));
            collection.insert(new BasicDBObject("a", 1));
            collection.createIndex(new BasicDBObject("a", 1), new BasicDBObject("unique", true));
            fail("should throw");
        } catch (WriteConcernException e) {
            System.out.println(e.getCommandResult());
            assertNotNull("didn't find error", e.getErrorMessage());
        } finally {
            client.close();
        }
    }
    // Output:
    // { "serverUsed" : "127.0.0.1:27017" , "ok" : 0.0 , "errmsg" : "E11000 duplicate key error index: test.foo.$a_1 dup key: { : 1 }" , "code" : 11000}
    // java.lang.AssertionError: didn't find error