code: @Deployment public void testReleaseTask() throws Exception {
    runtimeService.startProcessInstanceByKey("releaseTaskProcess");
    Task task=taskService.createTaskQuery().taskAssignee("fozzie").singleResult();
    assertNotNull(task);
    String taskId=task.getId();
    taskService.setAssignee(taskId,null);
    task=taskService.createTaskQuery().taskAssignee("fozzie").singleResult();
    assertNull(task);
    task=taskService.createTaskQuery().taskId(taskId).singleResult();
    assertNotNull(task);
    assertNull(task.getAssignee());
  }
  