SimpleRevisionServer implements RevisionServer { public Subscription registerListener(final Runnable listener) { listeners.add(listener); listener.run(); return new Subscription() { public void cancel() { listeners.remove(listener); } }; } @Inject  SimpleRevisionServer(@Nullable ConflictResolver conflictResolver,
			@Nullable ForeignKeyResolver foreignKeyResolver); Revision head(); void merge(Revision base, Revision fork); Subscription registerListener(final Runnable listener);  }
@Test public void registerListenerRunsListener() { server.registerListener(listener); verify(listener, times(1)).run(); }