### Question:
MetricsImpl implements Metrics { @Override public void add(long delta) { value.addAndGet(delta); } MetricsImpl(long start, long end, long initialValue);  MetricsImpl(long start, long end); @Override void add(long delta); @Override long getValue(); @Override long getStart(); @Override long getEnd();  }### Answer:
@Test public void add() { Metrics metrics = getMetrics(); metrics.add(100L); assertThat(metrics.getValue()).isEqualTo(100L); }