public String getExpression() {
        return expression;
    }
@Test
    void testDeserialization() throws JsonProcessingException {
        String json = "{\"type\":\"label\",\"expression\":\"test expression\"}";
        AbstractSelector actual = mapper.readValue(json, AbstractSelector.class);
        assertEquals(SelectorType.label.name(), actual.getType());
        ExpressionSelector selector = (ExpressionSelector) actual;
        assertEquals("test expression", selector.getExpression());
    }