@JsonValue
    @ThriftField(1)
    public Map<String, RuntimeMetric> getMetrics()
    {
        return Collections.unmodifiableMap(metrics);
    }
@Test(expectedExceptions = UnsupportedOperationException.class)
    public void testReturnUnmodifiedMetrics()
    {
        RuntimeStats stats = new RuntimeStats();
        stats.getMetrics().put(TEST_METRIC_NAME_1, new RuntimeMetric(TEST_METRIC_NAME_1, NONE));
    }