public static Map<String, Object> singletonMap(String key, Object value) {
        Map<String, Object> map = new HashMap<>(1);
        map.put(key, value);
        return map;
    }
@Test
    void singletonMap() {
        assertThat(CollectionUtil.singletonMap("key", "value"))
                .containsExactly(entry("key", "value"));
    }