### Question:
ValidatingArgumentSet implements ArgumentSet { @Override public boolean isEmpty() { return argumentSet.isEmpty(); } ValidatingArgumentSet(ArgumentSet argumentSet); @Override String get(int index); @Override int length(); @Override List<String> getAll(); @Override boolean isEmpty(); @Override boolean has(String argument); @Override String join(); @Override String[] toArray();  }### Answer:
@Test public void isEmpty() { validatingArguments.isEmpty(); verify(delegate).isEmpty(); }