如何使用 jest 模拟原始 const 值并恢复模拟？

Question

所以假设我有一个名为“config.js”的文件：

export const DELAY_SECONDS = 5;

在进行测试时：

// Ignore the delay when doing the tests.
jest.mock("/path/to/config", () => ({ DELAY_SECONDS: 0 }))

但我也想测试一下原始值是否有效：

it('should work with delay', () => {
    // Use original value implicitly.
    a_function_uses_DELAY_SECONDS()
    expect(...).toBe(...)
})

我怎样才能恢复那个模拟？或者有没有更好的方法来实现模拟？

我在下面尝试了一些方法，但它们都不起作用：

it('should work with delay', () => {
    jest.unmock() // Doesn't work at all, don't even know what does this method do.
    // Use original value implicitly.
    a_function_uses_DELAY_SECONDS()
    expect(...).toBe(...)
})

it('should work with delay', () => {
    jest.mock("/path/to/config", () => ({ DELAY_SECONDS: 5 })) // Call the mock again doesn't work
    // Use original value implicitly.
    a_function_uses_DELAY_SECONDS()
    expect(...).toBe(...)
})

it('should work with delay', () => {
    const config = require("/path/to/config").default;
    config.DELAY_SECONDS = 5; // Won't work, as it is a constant, cannot modify
    // Use original value implicitly.
    a_function_uses_DELAY_SECONDS()
    expect(...).toBe(...)
})

Answer 1

你可以使用jest.doMock(moduleName, factory, options)。

例如

config.js:

export const DELAY_SECONDS = 5;

main.js:

import { DELAY_SECONDS } from './config';

function main() {
  return DELAY_SECONDS;
}

export { main };

main.test.js:

describe('64473533', () => {
  beforeEach(() => {
    jest.resetModules();
  });
  it('should work with delay - original', () => {
    const { main } = require('./main');
    const actual = main();
    expect(actual).toBe(5);
  });
  it('should work with delay - mocked', () => {
    jest.doMock('./config', () => ({ DELAY_SECONDS: 0 }));
    const { main } = require('./main');
    const actual = main();
    expect(actual).toBe(0);
  });
});

单元测试结果：

 PASS  src/stackoverflow/64473533/main.test.js
  64473533
    ✓ should work with delay - original (445ms)
    ✓ should work with delay - mocked (2ms)

-----------|----------|----------|----------|----------|-------------------|
File       |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
-----------|----------|----------|----------|----------|-------------------|
All files  |      100 |      100 |      100 |      100 |                   |
 config.js |      100 |      100 |      100 |      100 |                   |
 main.js   |      100 |      100 |      100 |      100 |                   |
-----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        3.694s