如何使用模拟的定时器函数在C中对状态机进行单元测试？

#include <stdio.h>

// 模拟的定时器函数
int timer_expired = 0;

void set_timer(int time) {
    timer_expired = time;
}

int is_timer_expired() {
    return timer_expired <= 0;
}

void decrease_timer() {
    if (timer_expired > 0) {
        timer_expired--;
    }
}

// 状态机
typedef enum {
    STATE_IDLE,
    STATE_RUNNING,
    STATE_FINISHED
} State;

State current_state = STATE_IDLE;

void handle_idle_state() {
    printf("Idle state\n");
    // 处理Idle状态的逻辑
    if (is_timer_expired()) {
        current_state = STATE_RUNNING;
        set_timer(10); // 设置定时器为10
    }
}

void handle_running_state() {
    printf("Running state\n");
    // 处理Running状态的逻辑
    if (is_timer_expired()) {
        current_state = STATE_FINISHED;
    }
}

void handle_finished_state() {
    printf("Finished state\n");
    // 处理Finished状态的逻辑
}

void handle_state_machine() {
    switch (current_state) {
        case STATE_IDLE:
            handle_idle_state();
            break;
        case STATE_RUNNING:
            handle_running_state();
            break;
        case STATE_FINISHED:
            handle_finished_state();
            break;
        default:
            break;
    }
}

// 单元测试代码
void test_state_machine() {
    // 测试Idle状态
    current_state = STATE_IDLE;
    set_timer(0); // 设置定时器为0，立即触发状态转换
    handle_state_machine();

    // 测试Running状态
    current_state = STATE_RUNNING;
    set_timer(5); // 设置定时器为5
    handle_state_machine();

    // 测试Finished状态
    current_state = STATE_FINISHED;
    set_timer(0); // 设置定时器为0，立即触发状态转换
    handle_state_machine();
}

int main() {
    test_state_machine();
    return 0;
}