@Test(expected = UnsupportedOperationException.class)
public void getMarkersReturnsUnmodifiableSet() {

    final JavaValueFieldDefinition<Integer> underTest =
            JavaValueFieldDefinition.newInstance(KNOWN_JSON_POINTER, int.class, JsonValue::isNumber,
                    JsonValue::asInt, knownFieldMarkers);
    final Set<JsonFieldMarker> markers = underTest.getMarkers();
    markers.add(mock(JsonFieldMarker.class));
}