### Question:
TraceId { public static boolean isValid(CharSequence traceId) { return (traceId.length() == HEX_SIZE) && !INVALID.contentEquals(traceId) && BigendianEncoding.isValidBase16String(traceId); } private  TraceId(); static int getSize(); static int getHexLength(); static String getInvalid(); static String fromLongs(long idHi, long idLo); static byte[] bytesFromHex(String src, int srcOffset); static void copyHexInto(byte[] traceId, char[] dest, int destOffset); static boolean isValid(CharSequence traceId); static String bytesToHex(byte[] traceId); static long getTraceIdRandomPart(CharSequence traceId);  }### Answer:
@Test void isValid() { assertThat(TraceId.isValid(TraceId.getInvalid())).isFalse(); assertThat(TraceId.isValid(first)).isTrue(); assertThat(TraceId.isValid(second)).isTrue(); assertThat(TraceId.isValid("000000000000004z0000000000000016")).isFalse(); }