@Test
public void testJoinTransformWithEmptyMetricsLists() {

    Transform joinTransform = new JoinTransform();
    List<Metric> metrics_1 = new ArrayList<Metric>();
    List<Metric> metrics_2 = new ArrayList<Metric>();
    List<Metric> result = joinTransform.transform(null, metrics_1, metrics_2);
    assertEquals(result.size(), 0);
}