### Question:
ValidatingArgumentSet implements ArgumentSet { @Override public boolean has(String argument) { if (argument == null) { throw new IllegalArgumentException("Argument can not be null"); } return argumentSet.has(argument); } 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(expected = IllegalArgumentException.class) public void whenNullArgumentThanHasThrowsError() { validatingArguments.has(null); }
@Test public void has() { validatingArguments.has("example"); verify(delegate).has(eq("example")); }