Mocking of Node.js EcmaScript modules
npm install mock-import[NPMIMGURL]: https://img.shields.io/npm/v/mock-import.svg?style=flat
[BuildStatusURL]: https://github.com/coderaiser/mock-import/actions?query=workflow%3A%22Node+CI%22 "Build Status"
[BuildStatusIMGURL]: https://github.com/coderaiser/mock-import/workflows/Node%20CI/badge.svg
[LicenseIMGURL]: https://img.shields.io/badge/license-MIT-317BF9.svg?style=flat
[NPMURL]: https://npmjs.org/package/mock-import "npm"
[LicenseURL]: https://tldrlegal.com/license/mit-license "MIT License"
[CoverageURL]: https://coveralls.io/github/coderaiser/mock-import?branch=master
[CoverageIMGURL]: https://coveralls.io/repos/coderaiser/mock-import/badge.svg?branch=master&service=github
Mocking of Node.js EcmaScript Modules, similar to mock-require.
!Recording 2022-06-16 at 19 41 04
``sh`
npm i mock-import -D
Loaders used to get things working, so you need to run tests with:
`sh`
node --import mock-import/register test.js
mock-import uses transformSource hook, which replaces on the fly all imports with constants declaration:
`js`
const {readFile} = global.__mockImportCache.get('fs/promises');
mockImport adds new entry into Map, stopAll clears all mocks and reImport imports file again with new mocks applied.
`js
/ ✅ /
import fs from 'node:fs/promises';
/ ✅ /
import {readFile} from 'node:fs/promises';
/ ✅ /
import * as fs1 from 'node:fs/promises';
/ ✅ /
const {writeFile} = await import('fs/promses');
/ ✅ /
export * as fs2 from 'fs/promises';
/ ✅ /
export {readFile as readFile1} from 'fs/promises';
`
`js
/ ❌ /
export * from 'fs/promises';
// doesn't have syntax equivalent
`
works?As was said before, loaders used to get things working. This is experimental technology,mock-import
but most likely it wan't change. If it will will be adapted according to node.js API.
- loader hook intercepts into import process and get pathname of imported file;
- if pathname in reImports it is processed with 🐊Putout code transformer, changes all import calls to access to __mockImportsCache which is a Map filled with data set by mockImport call. And appends sourcemap at the end, so node can generate correct code coverage.
`diff`
-import glob from 'glob';
+const glob = global.__mockImportCache.get('./glob.js');
- if traceCache contains pathname it calls are traced with estrace;
Code like this
`js`
const f = () => {};
will be changed to
`js`
const f = () => {
try {
__estrace.enter('
} finally {
__estrace.exit('
}
};
Straight after loading and passed to traceImport stack will be filled with data this way:
`js`
__estrace.enter = (name, url, args) => stack.push([name, url, Array.from(args)]);
And when the work is done stack will contain all function calls.
- traceCache contains some paths current file will be checked for traced imports and change them to form ${path}?count=${count} to re-import them;
mock-import supports a couple env variables that extend functionality:
- MOCK_IMPORT_NESTED - transform each import statement so mock of module work in nested imports as well (slowdown tests a bit)
- name: string - module name;mock: object
- - mock data;
Mock import of a module.
Stop all mocks.
- name: string - name of a module
Fresh import of a module.
- name: string name of a modulestack: [fn, url, args]
- ;
Add tracing of a module.
- name: string - name of traced module
Apply tracing.
Enable nested imports, can slowdown tests;
Disable nested imports, use when you do not need nested imports support;
Let's suppose you have cat.js:
`js
import {readFile} from 'node:fs/promises';
export default async function cat() {
const readme = await readFile('./README.md', 'utf8');
return readme;
}
`
You can test it with 📼Supertape:
`js
import {createMockImport} from 'mock-import';
import {test, stub} from 'supertape';
const {
mockImport,
reImport,
stopAll,
} = createMockImport(import.meta.url);
test('cat: should call readFile', async (t) => {
const readFile = stub();
mockImport('fs/promises', {
readFile,
});
const cat = await reImport('./cat.js');
await cat();
stopAll();
t.calledWith(readFile, ['./README.md', 'utf8']);
t.end();
});
`
Now let's trace it:
`js
import {createMockImport} from 'mock-import';
import {test, stub} from 'supertape';
const {
mockImport,
reImport,
stopAll,
} = createMockImport(import.meta.url);
test('cat: should call readFile', async (t) => {
const stack = [];
traceImport('fs/promises', {
stack,
});
const cat = await reImport('./cat.js');
await cat();
stopAll();
const expected = [
['parse', 'parser.js:3', [
'const a = 5',
]],
['tokenize', 'tokenizer.js:1', [
'parser call',
'const a = 5',
]],
];
t.deepEqual(stack, expected);
t.end();
});
``
MIT