Extract JavaScript backend test resources to files

[riisi]

Migrate test_integration_test.py to use external test resource files instead of inlined rule_runner.write_files() calls. This follows the pattern established in the TypeScript backend and makes lockfiles easier to maintain with actual package manager commands.

Changes:

• Add test_resources/ directory with jest_project and mocha_project
• Add testutil.py with load_js_test_project() helper
• Refactor tests to load base projects and override specific files
• Remove unused fixtures (_find_lockfile_resource, jest_lockfile, etc.)

Ref: #22807

Summary of changes (Claude):

src/python/pants/backend/javascript/goals/
│
│  BEFORE                                     AFTER
│  ──────                                     ─────
│
│  test_integration_test.py                   test_integration_test.py
│  ├─ ~260 lines of inlined lockfiles,       ├─ loads via load_js_test_project()
│  │  package.json, source, BUILD content     ├─ overrides only per-test variations
│  ├─ hardcoded jest_dev_dependencies         ├─ reads deps from package.json (single source of truth)
│  └─ _find_lockfile_resource() fixtures      └─ removed unused fixtures
│
│  export_test.py                             export_test.py
│  └─ reads jest_resources/package-lock.json  └─ reads test_resources/jest_project/package-lock.json
│
│  jest_resources/  ──── DELETED ────────────→ (consolidated into test_resources/jest_project/)
│  ├─ BUILD            lockfiles only,
│  ├─ package.json     no source code
│  ├─ package-lock.json
│  ├─ pnpm-lock.yaml
│  └─ yarn.lock
│
│  mocha_resources/ ──── DELETED ────────────→ (consolidated into test_resources/mocha_project/)
│  ├─ BUILD
│  ├─ package.json
│  ├─ package-lock.json
│  ├─ pnpm-lock.yaml
│  └─ yarn.lock
│
│  (nothing)                                  testutil.py ─── NEW
│                                             └─ load_js_test_project(name, package_manager)
│                                                reads files from test_resources/, filters
│                                                lockfiles by package manager
│
│  (nothing)                                  test_resources/ ─── NEW
│                                             ├─ .gitignore, README.md
│                                             ├─ jest_project/    ← lockfiles from jest_resources/
│                                             │  ├─ BUILD, package.json, lockfiles (npm/pnpm/yarn)
│                                             │  └─ src/index.mjs, tests/index.test.js
│                                             └─ mocha_project/   ← lockfiles from mocha_resources/
│                                                ├─ BUILD, package.json, lockfiles (npm/pnpm/yarn)
│                                                └─ src/index.mjs, tests/index.test.mjs
│
│  BUILD                                      BUILD
│  ├─ test_integration_test deps:             ├─ test_integration_test deps:
│  │   ./jest_resources                       │   :jest_resources, :mocha_resources
│  │   ./mocha_resources                      ├─ export_test deps:
│  │   //...javascript:test_resources         │   :jest_resources
│  └─ export_test: no resource deps           ├─ resources(name="jest_resources",
│                                             │    sources=["test_resources/jest_project/**"])
│                                             └─ resources(name="mocha_resources",
│                                                  sources=["test_resources/mocha_project/**"])

[benjyw]

Looks good to me, but you can tell from my question that I am not very familiar with this code.

[benjyw]

For my education: what is the distinction between these jest_resources and the ones under test_resources/jest_project?

[sureshjoshi]

Just need to hold back on the merge here. There were a couple of things I saw briefly I didn't understand, but need to go back through the code properly and check out.

@riisi Is there any LLM disclosure here, for places for us to focus on reviewing?

Most of this looked good - but there were a couple of changes I didn't understand at a glance when I looked at this last week.

Need to carve out some time this week to review properly - it's mostly a mechanical change, but it's a big one.

[riisi]

I've removed the stale reference that @benjyw picked up. I've also tried to make the naming and location clearer / closer to consumers, and deps more granular. I think I was trying to minimise changes in the initial pass, but I think the clarity is better.

@sureshjoshi I'm using Claude here - I tried to make that implicit via commit message, but haven't been following the disclosure discussions sorry.