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import { describe, expect, it } from "vitest";
import { shuffle } from "./shuffle";
describe("shuffle", () => {
it("returns an array of the same length", () => {
const input = [1, 2, 3, 4, 5];
const result = shuffle(input);
expect(result).toHaveLength(input.length);
});
it("contains all original elements", () => {
const input = [1, 2, 3, 4, 5];
const result = shuffle(input);
expect(result.sort()).toEqual(input.sort());
});
it("does not mutate the original array", () => {
const input = [1, 2, 3, 4, 5];
const original = [...input];
shuffle(input);
expect(input).toEqual(original);
});
it("returns empty array for empty input", () => {
expect(shuffle([])).toEqual([]);
});
it("returns single element array unchanged", () => {
expect(shuffle([1])).toEqual([1]);
});
it("works with objects", () => {
const input = [{ id: 1 }, { id: 2 }, { id: 3 }];
const result = shuffle(input);
expect(result).toHaveLength(3);
expect(result.map((x) => x.id).sort()).toEqual([1, 2, 3]);
});
it("actually shuffles (statistical test)", () => {
const input = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
let sameOrderCount = 0;
const iterations = 100;
for (let i = 0; i < iterations; i++) {
const result = shuffle(input);
if (JSON.stringify(result) === JSON.stringify(input)) {
sameOrderCount++;
}
}
// Should very rarely keep original order (probability ~1/3628800)
expect(sameOrderCount).toBeLessThan(iterations * 0.1);
});
});
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