如何在玩笑中模拟导出的常量 [英] How to mock an exported const in jest

问题描述

我有一个依赖于导出的 const 变量的文件.此变量设置为 true 但如果需要，可以手动设置为 false 以防止下游服务请求时出现某些行为.

I have a file that relies on an exported const variable. This variable is set to true but if ever needed can be set to false manually to prevent some behavior if downstream services request it.

我不确定如何在 Jest 中模拟 const 变量，以便我可以更改它的值以测试 true 和 false 条件.

I am not sure how to mock a const variable in Jest so that I can change it's value for testing the true and false conditions.

示例:

//constants module
export const ENABLED = true;

//allowThrough module
import { ENABLED } from './constants';

export function allowThrough(data) {
  return (data && ENABLED === true)
}

// jest test
import { allowThrough } from './allowThrough';
import { ENABLED } from './constants';

describe('allowThrough', () => {
  test('success', () => {
    expect(ENABLED).toBE(true);
    expect(allowThrough({value: 1})).toBe(true);
  });

  test('fail, ENABLED === false', () => {
    //how do I override the value of ENABLED here?

    expect(ENABLED).toBe(false) // won't work because enabled is a const
    expect(allowThrough({value: 1})).toBe(true); //fails because ENABLED is still true
  });
});

推荐答案

如果您将 ES6 模块语法编译为 ES5，此示例将起作用，因为最终所有模块导出都属于同一个对象，可以修改.

This example will work if you compile ES6 modules syntax into ES5, because in the end, all module exports belong to the same object, which can be modified.

import { allowThrough } from './allowThrough';
import { ENABLED } from './constants';
import * as constants from './constants';

describe('allowThrough', () => {
    test('success', () => {
        constants.ENABLED = true;

        expect(ENABLED).toBe(true);
        expect(allowThrough({ value: 1 })).toBe(true);
    });

    test('fail, ENABLED === false', () => {
        constants.ENABLED = false;

        expect(ENABLED).toBe(false);
        expect(allowThrough({ value: 1 })).toBe(false);
    });
});

或者，您可以切换到原始的 commonjs require 函数，并在 jest.mock(...) 的帮助下这样做:

Alternatively, you can switch to raw commonjs require function, and do it like this with the help of jest.mock(...):

const mockTrue = { ENABLED: true };
const mockFalse = { ENABLED: false };

describe('allowThrough', () => {
    beforeEach(() => {
        jest.resetModules();
    });

    test('success', () => {
        jest.mock('./constants', () => mockTrue)
        const { ENABLED } = require('./constants');
        const { allowThrough } = require('./allowThrough');

        expect(ENABLED).toBe(true);
        expect(allowThrough({ value: 1 })).toBe(true);
    });

    test('fail, ENABLED === false', () => {
        jest.mock('./constants', () => mockFalse)
        const { ENABLED } = require('./constants');
        const { allowThrough } = require('./allowThrough');

        expect(ENABLED).toBe(false);
        expect(allowThrough({ value: 1 })).toBe(false);
    });
});

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