@Override
   public String evaluate(EvaluationContext evaluationContext, String... args) {
      return UUID.randomUUID().toString();
   }
@Test
   void testSimpleEvaluation() {
      // Compute uuid.
      UUIDELFunction function = new UUIDELFunction();
      String uuid = function.evaluate(null);

      // Check its RFC 4122 compliant.
      assertEquals(36, uuid.length());
      assertEquals(8, uuid.indexOf('-'));
      assertEquals(23, uuid.lastIndexOf('-'));
      assertEquals("-", uuid.substring(13, 14));
      assertEquals("4", uuid.substring(14, 15));
      assertEquals("-", uuid.substring(18, 19));
   }