apps/web/__tests__/player.test.ts

import { describe, expect, it } from "vitest";
import { midiToFreq, parseMidi, isPercussion, type ParsedNote } from "@/lib/jambuddy/player";

describe("midiToFreq", () => {
  it("maps A4 (69) to 440 Hz", () => {
    expect(midiToFreq(69)).toBeCloseTo(440, 3);
  });
  it("maps C4 (60) to ~261.6 Hz", () => {
    expect(midiToFreq(60)).toBeCloseTo(261.63, 1);
  });
  it("is an octave up 12 semitones", () => {
    expect(midiToFreq(81)).toBeCloseTo(midiToFreq(69) * 2, 3);
  });
});

describe("parseMidi", () => {
  it("throws a readable error for non-MIDI bytes", () => {
    expect(() => parseMidi(new Uint8Array([1, 2, 3]).buffer)).toThrow();
  });
});

describe("isPercussion", () => {
  it("flags GM channel 9 as percussion", () => {
    const drum: ParsedNote = {
      time: 0,
      midi: 36,
      duration: 0.1,
      velocity: 0.9,
      channel: 9,
    };
    expect(isPercussion(drum)).toBe(true);
  });
  it("does not flag a normal channel", () => {
    const bass: ParsedNote = {
      time: 0,
      midi: 40,
      duration: 0.2,
      velocity: 0.8,
      channel: 0,
    };
    expect(isPercussion(bass)).toBe(false);
  });
});