feat(js): m04 random and spawn with fixtures and tests

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

js/test/m04-random.test.js

@@ -0,0 +1,52 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { nextUint32, pure, map, flatMap, intBelow, run } from '../src/random.js'
+import { loadFixture, freeze } from './helpers.js'
+
+const fixtureTests = (name, f) => {
+  const fx = loadFixture(name)
+  fx.cases.forEach((c) =>
+    test(`m04 ${fx.function}: ${c.name}`, () => assert.deepStrictEqual(f(...freeze(c.args)), c.expected)))
+}
+
+fixtureTests('m04-random', (seed) => run(nextUint32, seed))
+fixtureTests('m04-int-below', (n, seed) => run(intBelow(n), seed))
+
+test('m04 the recorded steps chain: each step starts from the previous step\'s seed', () => {
+  const cases = loadFixture('m04-random').cases
+  cases.forEach((c, i) => {
+    if (!c.name.endsWith('-step-1')) assert.equal(c.args[0], cases[i - 1].expected[1])
+  })
+})
+
+test('m04 pure returns its value and leaves the seed alone', () =>
+  assert.deepStrictEqual(run(pure('x'), 99), ['x', 99]))
+
+test('m04 map applies f to the value and keeps the seed from the underlying step', () => {
+  const [v, s] = run(nextUint32, 5)
+  assert.deepStrictEqual(run(map(nextUint32, (x) => x + 1), 5), [v + 1, s])
+})
+
+test('m04 map with the identity function changes nothing', () =>
+  assert.deepStrictEqual(run(map(nextUint32, (x) => x), 5), run(nextUint32, 5)))
+
+test('m04 flatMap threads the seed through both steps', () => {
+  const [a, s1] = run(nextUint32, 5)
+  const [b, s2] = run(nextUint32, s1)
+  assert.deepStrictEqual(run(flatMap(nextUint32, (x) => map(nextUint32, (y) => [x, y])), 5), [[a, b], s2])
+})
+
+test('m04 flatMap with pure on the left or right changes nothing', () => {
+  assert.deepStrictEqual(run(flatMap(pure(3), (x) => map(nextUint32, (v) => v + x)), 5), run(map(nextUint32, (v) => v + 3), 5))
+  assert.deepStrictEqual(run(flatMap(nextUint32, pure), 5), run(nextUint32, 5))
+})
+
+test('m04 intBelow always lands in [0, n)', () => {
+  const draws = (n, seed, count) =>
+    count === 0 ? [] : ((([v, s]) => [v, ...draws(n, s, count - 1)])(run(intBelow(n), seed)))
+  ;[1, 2, 7, 400].forEach((n) =>
+    draws(n, 123, 50).forEach((v) => assert.ok(Number.isInteger(v) && v >= 0 && v < n, `${v} not in [0, ${n})`)))
+})
+
+test('m04 running a Random does not mutate anything: same seed, same answer', () =>
+  assert.deepStrictEqual(run(nextUint32, 8), run(nextUint32, 8)))

js/test/m04-spawn.test.js

@@ -0,0 +1,37 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { freeCells, spawnApple, tick, newGame } from '../src/spawn.js'
+import { advance } from '../src/rules.js'
+import { loadFixture, freeze } from './helpers.js'
+
+const fixtureTests = (name, f) => {
+  const fx = loadFixture(name)
+  fx.cases.forEach((c) =>
+    test(`m04 ${fx.function}: ${c.name}`, () => assert.deepStrictEqual(f(...freeze(c.args)), c.expected)))
+}
+
+fixtureTests('m04-free-cells', freeCells)
+fixtureTests('m04-spawn', spawnApple)
+fixtureTests('m04-new-game', newGame)
+
+// 3x2 board, one-cell snake, about to eat the apple at (1,0)
+const eating = freeze({
+  width: 3, height: 2, snake: [{ x: 0, y: 0 }], dir: 'Right', nextDir: 'Right',
+  apple: { x: 1, y: 0 }, seed: 0, score: 0, status: 'Playing', frame: 0,
+})
+
+test('m04 tick: eating the apple spawns a new one in the same step', () => {
+  // snake becomes [(1,0),(0,0)]; free cells are (2,0),(0,1),(1,1),(2,1); seed 0 draws 1144304738 % 4 = 2 -> (1,1)
+  assert.deepStrictEqual(tick(eating), {
+    ...eating, snake: [{ x: 1, y: 0 }, { x: 0, y: 0 }], apple: { x: 1, y: 1 }, score: 1, seed: 1831565813,
+  })
+})
+
+test('m04 tick is spawnApple after advance', () => assert.deepStrictEqual(tick(eating), spawnApple(advance(eating))))
+
+test('m04 tick leaves the seed alone when no apple needs spawning', () => {
+  const s = freeze({ ...eating, apple: { x: 2, y: 1 } })
+  assert.equal(tick(s).seed, 0)
+})
+
+test('m04 newGame is reproducible: same seed, same game', () => assert.deepStrictEqual(newGame(42), newGame(42)))