From 3dc49ed38c21eaa251fc307a328305ead9d33852 Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Fri, 28 Aug 2026 19:12:28 +0200
Subject: [PATCH] test(core): add audio synth and recorder tests

---
 tests/Chip8.Tests/AudioTests.cs | 112 ++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 tests/Chip8.Tests/AudioTests.cs

diff --git a/tests/Chip8.Tests/AudioTests.cs b/tests/Chip8.Tests/AudioTests.cs
new file mode 100644
index 0000000..a8743f7
--- /dev/null
+++ b/tests/Chip8.Tests/AudioTests.cs
@@ -0,0 +1,112 @@
+using System;
+using System.Linq;
+using System.Text;
+using Chip8.Core;
+using Chip8.Core.Audio;
+using Xunit;
+
+namespace Chip8.Tests;
+
+public class AudioTests
+{
+    [Fact]
+    public void wavHeaderDescribesMonoSixteenBitPcm()
+    {
+        var samples = new short[] { 1000, -1000, 500, -500 };
+        byte[] wav = WavFile.write(samples, 8000);
+
+        Assert.Equal("RIFF", Encoding.ASCII.GetString(wav, 0, 4));
+        Assert.Equal("WAVE", Encoding.ASCII.GetString(wav, 8, 4));
+        Assert.Equal("fmt ", Encoding.ASCII.GetString(wav, 12, 4));
+        Assert.Equal(1, BitConverter.ToInt16(wav, 20));
+        Assert.Equal(1, BitConverter.ToInt16(wav, 22));
+        Assert.Equal(8000, BitConverter.ToInt32(wav, 24));
+        Assert.Equal(16, BitConverter.ToInt16(wav, 34));
+        Assert.Equal("data", Encoding.ASCII.GetString(wav, 36, 4));
+        Assert.Equal(samples.Length * 2, BitConverter.ToInt32(wav, 40));
+        Assert.Equal(44 + samples.Length * 2, wav.Length);
+        Assert.Equal(1000, BitConverter.ToInt16(wav, 44));
+    }
+
+    [Theory]
+    [InlineData(0.4, 13106)]
+    [InlineData(2.0, 32767)]
+    [InlineData(-1.0, 0)]
+    public void amplitudeIsClampedAndScaled(double amplitude, int expected)
+    {
+        Assert.Equal((short)expected, AudioSynth.amplitudeToPcm(amplitude));
+    }
+
+    [Fact]
+    public void squareWaveHasHighThenLowHalfCycle()
+    {
+        short[] samples = AudioSynth.square(frequency: 1, sampleRate: 8, sampleCount: 8);
+        Assert.Equal(8, samples.Length);
+        Assert.All(samples[..4], sample => Assert.True(sample > 0));
+        Assert.All(samples[4..], sample => Assert.True(sample < 0));
+    }
+
+    [Fact]
+    public void decodePatternReadsMostSignificantBitFirst()
+    {
+        bool[] bits = AudioSynth.decodePattern(new byte[] { 0xAA });
+        Assert.True(bits[0]);
+        Assert.False(bits[1]);
+        Assert.True(bits[2]);
+        Assert.False(bits[7]);
+        Assert.Equal(AudioSynth.patternBits, bits.Length);
+    }
+
+    [Fact]
+    public void renderPatternFollowsBits()
+    {
+        var full = new byte[16];
+        Array.Fill(full, (byte)0xFF);
+        short[] loud = AudioSynth.renderPattern(full, playbackRate: 8, sampleRate: 8, sampleCount: 16);
+        Assert.All(loud, sample => Assert.True(sample > 0));
+
+        short[] quiet = AudioSynth.renderPattern(new byte[16], playbackRate: 8, sampleRate: 8, sampleCount: 16);
+        Assert.All(quiet, sample => Assert.True(sample < 0));
+    }
+
+    [Fact]
+    public void trackAccumulatesSamplesAndDuration()
+    {
+        var track = new AudioTrack(1000);
+        track.appendSilence(500);
+        track.appendSquare(200, 500);
+        Assert.Equal(1000, track.sampleCount);
+        Assert.Equal(1.0, track.durationSeconds, 3);
+
+        short[] samples = track.toSamples();
+        Assert.All(samples[..500], sample => Assert.Equal(0, sample));
+        Assert.Contains(samples[500..], sample => sample != 0);
+    }
+
+    [Fact]
+    public void trackProducesPlayableWav()
+    {
+        var track = new AudioTrack(8000);
+        track.appendSquare(440, 8000);
+        byte[] wav = track.toWav();
+        Assert.Equal("RIFF", Encoding.ASCII.GetString(wav, 0, 4));
+        Assert.Equal(44 + 8000 * 2, wav.Length);
+    }
+
+    [Fact]
+    public void recorderProducesSilenceForASilentProgram()
+    {
+        var machine = TestHarness.withProgram(Platform.Chip8, 0x1200);
+        var track = new AudioRecorder(sampleRate: 8000).record(machine, frames: 5, instructionsPerFrame: 4);
+        Assert.All(track.toSamples(), sample => Assert.Equal(0, sample));
+    }
+
+    [Fact]
+    public void recorderCapturesTheBeepRom()
+    {
+        var machine = new Machine(Quirks.modern(), 1);
+        machine.loadRom(TestHarness.romBytes("7-beep.ch8"));
+        var track = new AudioRecorder(sampleRate: 8000).record(machine, frames: 10, instructionsPerFrame: 11);
+        Assert.Contains(track.toSamples(), sample => sample != 0);
+    }
+}