javascript - 函数内部的 Jest 模拟函数

Question

我不知道如何在 jest 中模拟内部函数的返回值 我尝试了不同的方法。最后我找到了这个 answer 但出于某种原因不值得 mock ，这里是示例:

国家.js

export const countryList = () => [
      {
        label: '+244',
        value: 'Angola',
      }, // list of all possible countries very long...
 ];

export const getSortedCountryData = intlLang =>
  countriesList()
  .sort((compare, comparable) =>
    compare.value.localeCompare(comparable.value, intlLang, { sensitivity: 'base' }));

国家.test.js

import * as countyListHelper from './countries';

describe('countries list', () => {
  test('returns list of countries', () => {
    const mockFn = jest.mock();

    const expectedList = [
      {
        label: '+244',
        value: 'Angola',
      },
      {
        label: '+43',
        value: 'Austria',
      },
    ];

    mockFn.spyOn(countyListHelper, 'countriesList').mockReturnValue(expectedList);

    // console.log('if return value mocked correctly',
    // countyListHelper.countriesList() === expectedList); // true
    expect(countyListHelper.getSortedCountryData('en')).toEqual(expectedList);
    // shows error with received value list of all countries instead of mocked one
  });
});

请建议我任何可能的解决方案，为什么忽略内部函数的内部测试函数模拟返回值。从 Create React App 进行设置。

Answer 1

您链接到的问题当前接受的答案无效。我添加了一个 new answer带有解释和工作示例。

相同的概念适用于此:模拟替换函数的模块导出，以便能够在 getSortedCountryData 中模拟 countriesList为 countriesList 调用模块导出。

一个选择是将 countriesList 移动到它自己的模块中。

另一种选择是利用 "ES6 modules support cyclic dependencies automatically"因此将模块import 完全有效，这样您就可以为countriesList 调用module export:

国家.js

import * as countyListHelper from './countries';

export const countriesList = () => [
  {
    label: '+244',
    value: 'Angola',
  }, // list of all possible countries very long...
];

export const getSortedCountryData = intlLang =>
  countyListHelper.countriesList()
    .sort((compare, comparable) =>
      compare.value.localeCompare(comparable.value, intlLang, { sensitivity: 'base' }));

国家.test.js

import * as countyListHelper from './countries';

describe('countries list', () => {
  test('returns list of countries', () => {

    const expectedList = [
      {
        label: '+244',
        value: 'Angola',
      },
      {
        label: '+43',
        value: 'Austria',
      },
    ];

    const spy = jest.spyOn(countyListHelper, 'countriesList');
    spy.mockReturnValue(expectedList);

    expect(countyListHelper.getSortedCountryData('en')).toEqual(expectedList);  // Success!

    spy.mockRestore();
  });
});