如何在玩笑中模拟导出的const

Question

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

我不确定如何const在Jest中模拟变量，以便更改测试true和false条件的值。

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
  });
});

Answer 1

如果将ES6模块语法编译为ES5，则此示例将起作用，因为最后，所有模块导出都属于同一对象，可以对其进行修改。

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);
    });
});

另外，您可以切换到raw commonjs require函数，并借助以下方法做到这一点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);
    });
});