FileProvider implements Supplier<ImmutableSet<T>> { public static Builder builder() { return new Builder(); } FileProvider(ImmutableList<Path> rootPaths, Predicate<Path> predicate,
      Function<Path, T> reader); @Override ImmutableSet<T> get(); static Builder builder();  }
@Test(expected = IllegalArgumentException.class) public void testNoPaths() { FileProvider.builder().build(); }