### Question:
ResourceUtils { public static String formatWeakTag(String eTag) { String formattedTag = formatTag(eTag); if (formattedTag == null) { return null; } return "W/" + formattedTag; } private  ResourceUtils(); static String formatWeakTag(String eTag); static String formatTag(String eTag); static boolean matchTag(String eTag, String eTagHeaderValue); static long millisToSecond(long millisecond); static long secondToMillis(long second);  }### Answer:
@Test public void testFormatWeakTag() throws Exception { assertNull(ResourceUtils.formatWeakTag(null)); assertEquals("W/\"123-456789\"", ResourceUtils.formatWeakTag("123-456789")); try { ResourceUtils.formatWeakTag("123\"456789"); fail(); } catch (IllegalArgumentException e) { } }