pixi-demo/tests/chase/rng.test.ts

import { describe, expect, it } from "vitest";
import { createRng, normalizeSeed } from "../../src/stages/games/chase/logic/rng";

describe("chase rng", () => {
  it("generates the same sequence for the same seed", () => {
    const seed = 12345;
    const rngA = createRng(seed);
    const rngB = createRng(seed);

    const sequenceA = Array.from({ length: 5 }, () => rngA());
    const sequenceB = Array.from({ length: 5 }, () => rngB());

    expect(sequenceA).toEqual(sequenceB);
  });

  it("keeps createRng outputs in [0, 1)", () => {
    const rng = createRng(12345);
    const samples = Array.from({ length: 500 }, () => rng());

    for (const value of samples) {
      expect(value).toBeGreaterThanOrEqual(0);
      expect(value).toBeLessThan(1);
    }
  });

  it("matches a stable golden sequence for a fixed seed", () => {
    const rng = createRng(12345);
    const sequence = Array.from({ length: 5 }, () => rng());

    expect(sequence).toEqual([
      0.9797282677609473,
      0.3067522644996643,
      0.484205421525985,
      0.817934412509203,
      0.5094283693470061,
    ]);
  });

  it("produces different sequences for different seeds", () => {
    const rngA = createRng(12345);
    const rngB = createRng(12346);

    const sequenceA = Array.from({ length: 5 }, () => rngA());
    const sequenceB = Array.from({ length: 5 }, () => rngB());

    expect(sequenceA).not.toEqual(sequenceB);
  });

  it("normalizes undefined, empty and non-numeric string to numbers", () => {
    expect(typeof normalizeSeed(undefined)).toBe("number");
    expect(typeof normalizeSeed("")).toBe("number");
    expect(typeof normalizeSeed("abc")).toBe("number");
  });

  it("normalizes edge case seeds into uint32 semantics", () => {
    expect(normalizeSeed(NaN)).toBe(0x9e3779b9);
    expect(normalizeSeed(-1)).toBe(0xffffffff);
    expect(normalizeSeed(1.9)).toBe(1);
    expect(normalizeSeed("   ")).toBe(0x9e3779b9);
  });
});