Jest 26发布了一个基于@sinonjs/fake-timers的假定时器的新实现。
以前我使用const flushPromises = () => new Promise(setImmediate);
现在我想用
await new Promise(process.nextTick);
如本文所述：How to make Jest wait for all asynchronous code to finish execution before expecting an assertion但在某些情况下不起作用。
不工作时的示例代码（jest版本：27.5.1）：

class SuperFetch {
    public static async get(): Promise<string> {
        return 'never mind';
    }
}

class ClassForTest {
    public async get(): Promise<string> {
        return SuperFetch.get();
    }
}

带有遗留伪计时器的测试1（通过）：

jest.useFakeTimers('legacy');
describe('Test', () => {

    const flushPromises = (): Promise<void> => new Promise(setImmediate);
    
    test('should flush promise', async () => {
        SuperFetch.get = jest.fn().mockResolvedValue('test');
        const instance = new ClassForTest();
        let result;
        instance.get().then(x => {
            result = x;
        });

        jest.advanceTimersByTime(1000);
        await flushPromises();

        expect(result).toBe('test');
    });
});

使用现代伪计时器的测试2（失败）

jest.useFakeTimers('modern');
describe('Test', () => {
    test('should flush promise', async () => {
        SuperFetch.get = jest.fn().mockResolvedValue('test');
        const instance = new ClassForTest();
        let result;
        instance.get().then(x => {
            result = x;
        });

        jest.advanceTimersByTime(1000);
        await new Promise(process.nextTick);

        expect(result).toBe('test');
    });
});

失败并抛出**：“测试超时超过5000毫秒。**在调试期间，它在await new Promise(process.nextTick)上冻结