### Question:
Duration extends TimeBase<Duration> { @Override public Duration add(Duration d) { return new Duration(this.toSec() + d.toSec()); } Duration();  Duration(int secs, int nsecs);  Duration(double sec);  Duration(long nano); @Override Duration add(Duration d); @Override Duration subtract(Duration d); boolean sleep(); @Override Duration clone(); static Duration fromSec(double sec); static Duration fromNano(long nano); static Duration fromJsonString(String jsonString); static Duration fromJsonObject(JsonObject jsonObject); static final String TYPE; }### Answer:
@Test public void testAdd() { assertEquals(new Duration(10000001044l), d2.add(d3)); assertEquals(d1, empty.add(d1)); assertEquals(d2, empty.add(d2)); assertEquals(d3, empty.add(d3)); }