public void setExpression(String expression) {
        this.expression = expression;
    }
@Test
    void testSerialization() throws JsonProcessingException {
        ExpressionSelector selector = new ExpressionSelector();
        selector.setExpression("test expression");
        String actual = mapper.writeValueAsString(selector);
        assertTrue(actual.contains("\"type\":\"" + SelectorType.label.name() + "\""));
        assertTrue(actual.contains("\"expression\":\"test expression\""));
    }