@Override
    public Set<Long> calculateUsers(DelegateExecution execution, String param) {
        Set<Long> groupIds = StrUtils.splitToLongSet(param);
        List<BpmUserGroupDO> groups = userGroupService.getUserGroupList(groupIds);
        return convertSetByFlatMap(groups, BpmUserGroupDO::getUserIds, Collection::stream);
    }
@Test
    public void testCalculateUsers() {
        // 准备参数
        String param = "1,2";
        // mock 方法
        BpmUserGroupDO userGroup1 = randomPojo(BpmUserGroupDO.class, o -> o.setUserIds(asSet(11L, 12L)));
        BpmUserGroupDO userGroup2 = randomPojo(BpmUserGroupDO.class, o -> o.setUserIds(asSet(21L, 22L)));
        when(userGroupService.getUserGroupList(eq(asSet(1L, 2L)))).thenReturn(Arrays.asList(userGroup1, userGroup2));

        // 调用
        Set<Long> results = strategy.calculateUsers(null, param);
        // 断言
        assertEquals(asSet(11L, 12L, 21L, 22L), results);
    }