public abstract String getAcknowledgmentType();
@Test
    public void testGetAcknowledgmentType() {
        instance = new MllpNegativeAcknowledgementExceptionStub(
                EXCEPTION_MESSAGE, HL7_MESSAGE_BYTES, HL7_ACKNOWLEDGEMENT_BYTES, LOG_PHI_TRUE);

        assertNull(instance.getAcknowledgmentType());
    }