### Question:
CharSet { public boolean contains(char ch) { return chars.contains(ch); } private  CharSet(String chars); static CharSet getInstance(String chars); boolean contains(char ch);  }### Answer:
@Test public void WS() { assertTrue(WS.contains(' ')); }
@Test public void WORD() { assertTrue(WORD.contains('a')); assertTrue(WORD.contains('c')); assertTrue(WORD.contains('A')); assertTrue(WORD.contains('Z')); assertTrue(WORD.contains('2')); assertTrue(WORD.contains('9')); }