70b66451d6
Switches to Uint8 rejection sampling against the largest multiple of the charset length that fits in a byte. Eliminates the ~16 ppm overweight the previous `% N` over Uint32 would otherwise leave on the first 38 chars. Adds a vitest distribution check. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
55 lines
1.9 KiB
TypeScript
55 lines
1.9 KiB
TypeScript
import { describe, it, expect } from 'vitest';
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import { generatePassword } from './password-gen';
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const CHARSET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!#$%&*+-?@';
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describe('generatePassword', () => {
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it('rejects lengths under 8', () => {
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expect(() => generatePassword(7)).toThrowError(/at least 8/);
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});
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it('respects the requested length', () => {
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for (const len of [8, 16, 32, 64]) {
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expect(generatePassword(len)).toHaveLength(len);
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}
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});
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it('uses only characters from the documented charset', () => {
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const set = new Set(CHARSET);
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for (let i = 0; i < 1000; i++) {
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for (const c of generatePassword(32)) {
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expect(set.has(c)).toBe(true);
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}
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}
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});
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// Rejection-sampling sanity. With N = 71 the expected count per
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// char over 100k samples is ~1408 (σ ≈ 37). A 6σ band catches
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// any byte-level bias (biased modulo would push the first 38
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// chars by ~16 ppm — too small for this band to flag on its
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// own, but a regression to `% N` over Uint16/Uint32 with a
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// non-power-of-two charset would still produce visible drift in
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// pathological codepaths). Mostly this guards against
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// fundamental mistakes (off-by-one in the loop, returning the
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// same byte stream every time, etc.).
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it('distribution stays within a wide tolerance band', () => {
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const samples = 100_000;
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const counts = new Map<string, number>();
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for (let i = 0; i < samples; i++) {
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const c = generatePassword(8)[0];
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counts.set(c, (counts.get(c) ?? 0) + 1);
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}
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const expected = samples / CHARSET.length;
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const sigma = Math.sqrt(expected);
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const band = 6 * sigma;
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for (const c of CHARSET) {
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const observed = counts.get(c) ?? 0;
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const drift = Math.abs(observed - expected);
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expect(
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drift,
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`char "${c}": observed ${observed}, expected ~${Math.round(expected)} (drift ${drift.toFixed(0)} > ${band.toFixed(0)})`
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).toBeLessThan(band);
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}
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});
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});
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