public synchronized void complete(long taskId) throws IllegalArgumentException {
        TaskStatus status = tasks.remove(taskId);
        if (status == null) {
            throw new IllegalArgumentException("TaskId is not in map:" + taskId);
        }
    }
@Test
    public void testBadId() throws Exception {
        ServerStatus status = new ServerStatus("", 0);
        assertThrows(IllegalArgumentException.class, () -> {
            status.complete(2);
        });
    }