Java中延迟"运行一次"初始化的方法,以及单元测试的覆盖

public class Singleton {
    private static Singleton instance;

    private Singleton() {
        // 构造函数私有化，防止外部实例化
    }

    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

public class SingletonTest {
    private Singleton singleton;

    @Before
    public void setUp() {
        singleton = Singleton.getInstance();
    }

    @Test
    public void testSingleton() {
        Singleton anotherSingleton = Singleton.getInstance();
        assertSame(singleton, anotherSingleton);
    }
}