MarkTool { public boolean isValidFilter() { return !shownWords.isEmpty(); } MarkTool(final List<T> words);  MarkTool(final WordFilter filter, final List<T> words); List<T> getShownWords(); boolean isValidFilter(); int getKnown(); int getUnknown(); int getUnseenUnfiltered(); int getUnseenFiltered(); static boolean isShown(final WordFilter filter, final W w);  }
@Test public void testEmptyIsValidFilter() { assertFalse(emptyTarget.isValidFilter()); }
@Test public void testIsValidFilter() { assertTrue(target.isValidFilter()); }