code: @Deployment public void test(){
    ProcessInstance pi=runtimeService.startProcessInstanceByKey("skipExpressionUserTask");
    List<Task> tasks=taskService.createTaskQuery().list();
    assertEquals(1,tasks.size());
    taskService.complete(tasks.get(0).getId());
    assertEquals(0,taskService.createTaskQuery().list().size());
    Map<String,Object> variables2=new HashMap<String,Object>();
    variables2.put("_ACTIVITI_SKIP_EXPRESSION_ENABLED",true);
    variables2.put("skip",false);
    runtimeService.startProcessInstanceByKey("skipExpressionUserTask",variables2);
    List<Task> tasks2=taskService.createTaskQuery().list();
    assertEquals(1,tasks2.size());
    taskService.complete(tasks2.get(0).getId());
    assertEquals(0,taskService.createTaskQuery().list().size());
    Map<String,Object> variables3=new HashMap<String,Object>();
    variables3.put("_ACTIVITI_SKIP_EXPRESSION_ENABLED",true);
    variables3.put("skip",true);
    ProcessInstance pi3=runtimeService.startProcessInstanceByKey("skipExpressionUserTask",variables3);
    List<Task> tasks3=taskService.createTaskQuery().list();
    assertEquals(0,tasks3.size());
  }
  