Testing configuration

Test precedence, environment handling and validation without touching process.env or the disk, because resolve() takes every layer as an argument.

resolve reads nothing ambient, so a test states the world it is about: the flags typed, the environment, the config file's contents. There is nothing to restore afterwards, and nothing leaks between tests.

config-test.mjs

import assert from 'node:assert/strict';

import { resolve, validate } from 'seniority';

const specs = { region: { type: 'string', default: 'us-1' }, verbose: { type: 'boolean' } };
const world = (over = {}) => ({ flags: {}, env: {}, envPrefix: 'APP', ...over });

// The default, when nothing else speaks.
assert.equal(resolve(specs, world()).values.region, 'us-1');

// The environment beats the config file, and says so.
const r = resolve(specs, world({ env: { APP_REGION: 'eu-3' }, config: { path: 'c.json', data: { region: 'eu-2' } } }));
assert.deepEqual(r.provenance.region, { source: 'env', location: 'APP_REGION' });

// A variable for an option nobody declared is ignored.
assert.deepEqual(resolve(specs, world({ env: { APP_DEBUG: '1' } })).values, { region: 'us-1' });

// An unclear boolean is an error, not a truthy string.
assert.throws(() => resolve(specs, world({ env: { APP_VERBOSE: 'maybe' } })), /is not a boolean/);

// Validation points at the source.
const bad = resolve({ port: { type: 'number' } }, world({ config: { path: 'c.json', data: { port: 'eighty' }, lines: { port: 4 } } }));
assert.deepEqual(validate({ port: { type: 'number' } }, bad).map((v) => v.message), ['`port` must be a number; `c.json:4` set it to `"eighty"`']);

console.log('ok');

node config-test.mjs

ok

For discovery, search takes injected exists and realpath functions, so even the upward walk can be tested over an imaginary tree.