feat(js): m01 util and m02 model with tests, fixtures, purity audit

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

js/test/m01-util.test.js

@@ -0,0 +1,47 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { range, dropLast, contains, pipe, compose, deepFreeze } from '../src/util.js'
+import { freeze } from './helpers.js'
+
+test('m01 range(0) is empty', () => assert.deepEqual(range(0), []))
+test('m01 range(3) counts from zero up to n-1', () => assert.deepEqual(range(3), [0, 1, 2]))
+
+test('m01 dropLast of an empty list is empty', () => assert.deepEqual(dropLast([]), []))
+test('m01 dropLast removes only the last element', () => assert.deepEqual(dropLast([1, 2, 3]), [1, 2]))
+test('m01 dropLast leaves its input untouched', () => {
+  const xs = freeze([1, 2, 3])
+  assert.deepEqual(dropLast(xs), [1, 2])
+  assert.deepEqual(xs, [1, 2, 3])
+})
+
+const sameParity = (a, b) => a % 2 === b % 2
+test('m01 contains finds an element using the supplied equality', () =>
+  assert.equal(contains([1, 2, 3], 5, sameParity), true))
+test('m01 contains is false when no element is equal', () =>
+  assert.equal(contains([2, 4], 3, sameParity), false))
+test('m01 contains is false for an empty list', () =>
+  assert.equal(contains([], 1, (a, b) => a === b), false))
+test('m01 contains compares structurally when given a structural equality', () => {
+  const eq = (a, b) => a.x === b.x && a.y === b.y
+  assert.equal(contains(freeze([{ x: 1, y: 2 }]), { x: 1, y: 2 }, eq), true)
+})
+
+test('m01 pipe threads a value through functions left to right', () =>
+  assert.equal(pipe(2, (x) => x + 1, (x) => x * 10), 30))
+test('m01 pipe with no functions returns the value', () => assert.equal(pipe(5), 5))
+
+test('m01 compose applies functions right to left', () =>
+  assert.equal(compose((x) => x * 10, (x) => x + 1)(2), 30))
+test('m01 compose with no functions is the identity', () => assert.equal(compose()(5), 5))
+
+test('m01 deepFreeze freezes nested objects and arrays', () => {
+  const o = deepFreeze({ a: { b: [1, { c: 2 }] } })
+  assert.ok(Object.isFrozen(o))
+  assert.ok(Object.isFrozen(o.a))
+  assert.ok(Object.isFrozen(o.a.b))
+  assert.ok(Object.isFrozen(o.a.b[1]))
+})
+test('m01 deepFreeze returns the same object it was given', () => {
+  const o = {}
+  assert.equal(deepFreeze(o), o)
+})