thrown:undefined when using settimout in promise

did anybody get the same error when i use promise and setTimeout to mock delay case, but it doesn’t work. I have no clue to resolve it. system: node v12.14.1 npm v6.13.4 jest 24.9.0

// index.js
export const fn = () => {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve('it didnt work');
        }, 0);
    });
}

// index.test.js
const { fn } = require('./a');
describe('aa', () => {
    test('aaa', async () => {
        const data = await fn();
        return expect(data).toEqual('it didnt work');
    });
});

=>result error:
thrown: undefined
at new Spec (node_modules/jest-jasmine2/build/jasmine/Spec.js:116:22)

[SimenB]

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[nancy-Gao]

Thank you so much. I resovled it! The reason of why Promise doesn’t work is that the project imports a file who includes Promise and throws error at the entry file.