Testing resolution without process.env

Test what your program would run — on Linux, on Windows, with a hostile PATH — by passing a literal runtime instead of mutating process.env.

Every bellpull function takes the environment as an argument, so a test states the world it is about instead of editing the one it runs in. Nothing to restore afterwards, nothing that leaks between tests, and Windows rules run on a Mac:

resolution-test.mjs

import assert from 'node:assert/strict';

import { searchPath, whichSync } from 'bellpull/which';

import { install } from './tools.mjs';

install();
const cwd = process.cwd();
const linux = (PATH) => ({ runtime: { platform: 'linux', env: { PATH }, cwd } });

// The PATH order decides, and the answer says which entry won.
assert.equal(whichSync('greet', linux(`${cwd}/vendor/bin:${cwd}/bin`))?.from, `${cwd}/vendor/bin`);
assert.equal(whichSync('greet', linux(`${cwd}/bin:${cwd}/vendor/bin`))?.from, `${cwd}/bin`);

// A relative entry is never searched, even when the tool is right there.
assert.equal(whichSync('greet', linux('bin')), undefined);
assert.deepEqual(searchPath(linux('bin')), [{ raw: 'bin', skipped: 'relative' }]);

// Windows reads PATH under whatever case it was spelled, and splits it on `;`.
const windows = { runtime: { platform: 'win32', env: { Path: 'C:\\a;C:\\b' }, cwd: 'C:\\work' } };
assert.deepEqual(searchPath(windows).map((e) => e.dir), ['C:\\work', 'C:\\a', 'C:\\b']);

console.log('ok');

node resolution-test.mjs

ok

For the spawning half, run() takes the same runtime: the child is spawned with its env and cwd, so a test that controls PATH controls which binary runs. bellpull's own suite drives the Windows branch of bellpull/cross-spawn from a Mac the same way.