#[test]
    fn get_voi_lut_function() {
        use super::voi_lut_function;

        let mut obj = FileDicomObject::new_empty_with_meta(
            FileMetaTableBuilder::new()
                .transfer_syntax(uids::EXPLICIT_VR_LITTLE_ENDIAN)
                .media_storage_sop_class_uid(uids::ENHANCED_MR_IMAGE_STORAGE)
                .media_storage_sop_instance_uid("2.25.145929179730251416957282651365760465911")
                .build()
                .unwrap(),
        );

        // Returns None if not present
        assert_eq!(voi_lut_function(&obj).unwrap(), None);

        obj.put(DataElement::new(
            tags::VOILUT_FUNCTION,
            VR::CS,
            PrimitiveValue::Empty,
        ));
        // Returns None if empty
        assert_eq!(voi_lut_function(&obj).unwrap(), None);

        obj.put(DataElement::new(tags::VOILUT_FUNCTION, VR::CS, "LINEAR"));

        // Returns the value
        assert_eq!(
            voi_lut_function(&obj).unwrap(),
            Some(vec!["LINEAR".to_string()])
        );

        obj.remove_element(tags::VOILUT_FUNCTION);

        // per-frame functional groups
        obj.put(DataElement::new(
            tags::PER_FRAME_FUNCTIONAL_GROUPS_SEQUENCE,
            VR::SQ,
            DataSetSequence::from(vec![InMemDicomObject::from_element_iter([
                DataElement::new(tags::VOILUT_FUNCTION, VR::CS, "LINEAR_EXACT"),
            ])]),
        ));

        assert_eq!(
            voi_lut_function(&obj).unwrap(),
            Some(vec!["LINEAR_EXACT".to_string()])
        );
    }