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tests/player/playlist.test.ts

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import { describe, expect, it } from 'vitest';
import { nextIndex, prevIndex } from '~/player/playlist';

describe('nextIndex', () => {
  it('advances within bounds', () => {
    expect(nextIndex(0, 3, false)).toBe(1);
    expect(nextIndex(1, 3, false)).toBe(2);
  });
  it('wraps to 0 at the end when loop is on', () => {
    expect(nextIndex(2, 3, true)).toBe(0);
  });
  it('returns null at the end when loop is off', () => {
    expect(nextIndex(2, 3, false)).toBeNull();
  });
  it('returns null for an empty list', () => {
    expect(nextIndex(0, 0, true)).toBeNull();
  });
});

describe('prevIndex', () => {
  it('steps back within bounds', () => {
    expect(prevIndex(2, 3, false)).toBe(1);
  });
  it('wraps to the last index when loop is on', () => {
    expect(prevIndex(0, 3, true)).toBe(2);
  });
  it('returns null at the start when loop is off', () => {
    expect(prevIndex(0, 3, false)).toBeNull();
  });
});