René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"test-runner: `require`ing a mocked dual-package gets the original instead of the mock","articleBody":"### Version\n\n22.15\n\n### Platform\n\n```text\nDarwin MacBook-Pro.local 24.4.0 Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:47 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6000 arm64\n```\n\n### Subsystem\n\nnode:mock\n\n### What steps will reproduce the bug?\n\n\nThe issue is for packages that expose esm `module` and cjs `main`.  See Repo: https://github.com/sloops77/node-mock-bug for more examples\n\nRather than create my own package the examples below use the `nanoid` 3.x package. The linked repo also shows that it is reproducible for the ethers package (which also exposes `module` and `main`).\n\n```json\n// snippet of package.json from nanoid\n{\n  \"name\": \"nanoid\",\n  \"version\": \"3.3.11\",\n  \"description\": \"A tiny (116 bytes), secure URL-friendly unique string ID generator\",\n  \"type\": \"module\",\n  \"main\": \"index.cjs\",\n  \"module\": \"index.js\",\n  ...\n```\n\n```js\n// test.js\nconst {describe, it, mock} = require(\"node:test\");\nconst assert = require(\"node:assert\");\n\nmock.module('nanoid', {\n  namedExports: {\n    nanoid() {\n      return '1234'\n    }\n  },\n});\n\n\ntest('mocking problem in cjs', () => {\n  const {nanoid} = require('nanoid')\n  assert.strictEqual(nanoid(), '1234'); // fails test because cjs is not mocked\n})\n\ntest('mocking works for esm', async () => {\n  const {nanoid} = await import('nanoid')\n  assert.strictEqual(nanoid(), '1234'); // works as it should\n})\n\n```\n\n\n### How often does it reproduce? Is there a required condition?\n\n1. For imported packages it seems 100% consistent. It also occurs for a module mock that uses `defaultExport`.\n2. Node core modules do not reproduce this issue\n\n### What is the expected behavior? Why is that the expected behavior?\n\nCJS & MJS files should receive a mocked module\n\n### What do you see instead?\n\nCJS files receive the original module, not the mock. MJS files are fine as they receive the mock.\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/sloops77","@type":"Person","name":"sloops77"},"datePublished":"2025-05-08T11:30:49Z","url":"https://github.com/nodejs/node/issues/58231"}