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