public static FEELFunction[] getFunctions() {
        return FUNCTIONS;
    }
@Test
    void getFunctions() {
        // This test is aimed at verify that all the "INSTANCE" fields are correctly populated, referring to the same class they are defined in
        Set< Class<? extends FEELFunction>> verifiedClasses = Stream.of(FUNCTIONS).map(this::validateFunction)
                .filter(Objects::nonNull)
                .collect(Collectors.toUnmodifiableSet());
        assertEquals(FUNCTIONS.length, verifiedClasses.size());
    }