javascript - Jest 模拟和错误处理 - Jest 测试跳过我函数的 "catch"

Question

我正在创建一个 Jest 测试来测试是否记录了用于 superFetch 函数错误处理的指标。我的方法是为 retryFetch 创建一个模拟函数并返回一个 Promise 拒绝事件。我希望它能进入 superFetch 捕获，但它会一直在 superFetch 中结束。我该如何处理 superFetch catch 中的错误？

这些是函数:

// file: fetches.js
export function retryFetch(url) {
    return new Promise((resolve, reject) => {
          fetch(url).then(response => {
                if (response.ok) {
                     resolve(response);
                     return;
                }
                throw new Error();
          }).catch(error => {
                createSomething(error).then(createSomething => {
                   reject(createSomething);
                });
                return;
          });
    });
});

export function superFetch(url, name, page) {
    return retryFetch(url)
        .then(response => {
            return response;
        }).catch(error => {
            Metrics.logErrorMetric(name, page);
            throw error;
        });
}

我的 Jest 测试:

import * as fetch from '../../src/utils/fetches';

    describe('Fetch fails', () => {
        beforeEach(() => {
            fetch.retryFetch = jest.fn(() => Promise.reject(new Error('Error')));
        });

        it('error metric is logged', () => {
            return fetch.superFetch('url', 'metric', 'page').then(data => {
                expect(data).toEqual(null);
                // received data is {"ok": true};
                // why is it even going here? im expecting it to go skip this and go to catch

            }).catch(error => {
                // this is completely skipped. but I'm expecting this to catch an error
                // received error is null, metric was not called
                expect(Metrics.logErrorMetric).toHaveBeenCalled();
                expect(error).toEqual('Error');
            });
        });
    });

Answer 1

问题是你覆盖了导出模块中的函数，但是 superFetch 使用了模块内部的原始函数，所以覆盖不会有任何效果。

你可以像这样直接模拟fetch:

global.fetch = jest.mock(()=> Promise.reject())