tests/integration/midi.test.js

import { describe, it, expect } from "vitest";
import { generateMidi } from "../../src/controller/tracks.js";
describe("integration: midi-writer-js", () => {
  /** @test {generateMidi} */
  it("emits a real MIDI binary with the expected header from a realistic solution", () => {
    const part = {
      solution: {
        note_0_0: 60, // C4
        note_0_1: -2, // tie -> extends C4
        note_0_2: 64, // E4
        note_0_3: -1, // rest
      },
      numSubBeats: 4,
      subdivision: 1,
      numerator: 4,
      denominator: 4,
      key: 0,
      mode: "major",
    };
    const step3Params = { voices: 1, voice: [{ instrument: 0 }] };
    const { combinedB64, voicesB64 } = generateMidi([part], step3Params, 120);
    expect(voicesB64).toHaveLength(1);
    // MIDI files start with "MThd" header chunk.
    const bytes = Uint8Array.from(atob(combinedB64), (c) => c.charCodeAt(0));
    const header = String.fromCharCode(...bytes.slice(0, 4));
    expect(header).toBe("MThd");
    // A "MTrk" chunk must be present somewhere after the header.
    const ascii = String.fromCharCode(...bytes);
    expect(ascii).toContain("MTrk");
  });
  /** @test {generateMidi} */
  it("produces one MTrk per voice in the combined file when multiple voices are present", () => {
    const part = {
      solution: { note_0_0: 60, note_1_0: 67 }, // C4 + G4 simultaneously
      numSubBeats: 1,
      subdivision: 1,
      numerator: 1,
      denominator: 4,
      key: 0,
      mode: "major",
    };
    const step3Params = {
      voices: 2,
      voice: [{ instrument: 0 }, { instrument: 42 }],
    };
    const { combinedB64, voicesB64 } = generateMidi([part], step3Params, 120);
    expect(voicesB64).toHaveLength(2);
    const bytes = Uint8Array.from(atob(combinedB64), (c) => c.charCodeAt(0));
    const ascii = String.fromCharCode(...bytes);
    // Combined file should contain two track chunks (one per voice).
    const trackCount = ascii.match(/MTrk/g)?.length ?? 0;
    expect(trackCount).toBe(2);
  });
});