feat: ship a Jest mock backed by node:crypto

[AttayR]

Follows up on discussion #800, where adding mocks for Jest was suggested.

Problem

Jest runs in Node, where the native module doesn't exist, so any app test that imports react-native-quick-crypto (directly or through its own code) throws. Today every app has to hand-write stubs for the functions it uses.

Change

Ship a mock at react-native-quick-crypto/jest. Node already implements the crypto API this library brings to React Native, so the mock forwards to node:crypto instead of stubbing functions. Tests get real hashes, ciphertexts and signatures, and app code runs unchanged.

// jest.setup.js
jest.mock('react-native-quick-crypto', () =>
  require('react-native-quick-crypto/jest'),
);

• Default and named exports both work; install() is a no-op (Node already has globalThis.crypto and Buffer).
• APIs Node doesn't have (BLAKE3, ML-KEM, …) are undefined; the guide shows how to extend the mock for those.
• jest is added to files so it's published. It's plain CommonJS because Jest doesn't transform node_modules by default.

Files

• packages/react-native-quick-crypto/jest/index.js: the mock
• packages/react-native-quick-crypto/test/jestMock.test.ts: default/named exports, SHA-256 vector, AES-256-GCM round trip, subtle.sign/verify (HMAC)
• docs/content/docs/guides/testing-with-jest.mdx and meta.json: new guide
• eslint.config.mjs: lets ESLint parse the CommonJS mock (allowDefaultProject plus a CommonJS override), since it sits outside tsconfig

Testing

• jest: 19/19 (existing tests plus 4 new)
• eslint "**/*.{js,ts,tsx}", prettier --check on the changed files, tsc --noEmit: clean
• Checked the documented setup from a separate project that imports the package by name, with the real entry point replaced by one that throws. The tests pass through the mock, including subtle.verify resolving to true and argon2 being available (Node 24.7+).

I targeted main only. Happy to backport to 0.x if you want it there too.

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[boorad]

Thanks for this, @AttayR! Forwarding to node:crypto instead of stubbing each function is a good call.

I pushed a small follow-up commit (94d5a45) to your branch:

• CryptoKey export: without it, app code doing x instanceof CryptoKey (with CryptoKey imported from the package) threw under the mock. It now comes from globalThis.CryptoKey, because Node doesn't put it on crypto.webcrypto. The HMAC test also checks the generated key against it.
• Shorter header comment: it's one line now that points to the guide, which already covers usage.
• Guide callout: it now also lists xsalsa20, randomUUIDv7, and the hkdfExtract/hkdfExpand helpers among the APIs the mock doesn't provide.

Jest passes 19/19, and ESLint and Prettier are clean. No need to backport to 0.x.