@Test public void countsArtists() { assertEquals(1, order.countMusicians()); }
public abstract long countMusicians();
Order { public abstract long countMusicians(); }
Order { public abstract long countMusicians(); Order(List<Album> albums); }
Order { public abstract long countMusicians(); Order(List<Album> albums); abstract long countRunningTime(); abstract long countMusicians(); abstract long countTracks(); }
Order { public abstract long countMusicians(); Order(List<Album> albums); abstract long countRunningTime(); abstract long countMusicians(); abstract long countTracks();  }