### Question:
SetDynamicCompositeCancellable implements DynamicCompositeCancellable { @Override public void cancel() { if (cancelledUpdater.compareAndSet(this, 0, 1)) { cancelAll(); } } SetDynamicCompositeCancellable();   SetDynamicCompositeCancellable(int initialSize); @Override void cancel(); @Override boolean add(Cancellable toAdd); @Override boolean remove(Cancellable toRemove); @Override boolean isCancelled();  }### Answer:
@Test public void testCancel() { SetDynamicCompositeCancellable c = new SetDynamicCompositeCancellable(); Cancellable cancellable = mock(Cancellable.class); c.add(cancellable); c.cancel(); verify(cancellable).cancel(); c.remove(cancellable); }