From dd55300b3104eaf958cc38a5529e2d96e83d97ae Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Thu, 27 Aug 2026 21:54:59 +0200
Subject: [PATCH] test(core): add machine state and ROM loading tests

---
 tests/Chip8.Tests/MachineTests.cs | 121 ++++++++++++++++++++++++++++++
 tests/Chip8.Tests/RomTests.cs     |  36 +++++++++
 2 files changed, 157 insertions(+)
 create mode 100644 tests/Chip8.Tests/MachineTests.cs
 create mode 100644 tests/Chip8.Tests/RomTests.cs

diff --git a/tests/Chip8.Tests/MachineTests.cs b/tests/Chip8.Tests/MachineTests.cs
new file mode 100644
index 0000000..9ff5c16
--- /dev/null
+++ b/tests/Chip8.Tests/MachineTests.cs
@@ -0,0 +1,121 @@
+using System;
+using Chip8.Core;
+using Xunit;
+
+namespace Chip8.Tests;
+
+public class MachineTests
+{
+    [Fact]
+    public void resetLoadsFontAndProgramCounter()
+    {
+        var machine = new Machine(Quirks.modern(), 1);
+        Assert.Equal(Machine.programStart, machine.pc);
+        Assert.Equal(0xF0, machine.memory[0x50]);
+        Assert.Equal(0x80, machine.memory[0x50 + 5 * 0xF + 4]);
+    }
+
+    [Fact]
+    public void loadRomCopiesBytesToProgramArea()
+    {
+        var machine = new Machine(Quirks.modern(), 1);
+        machine.loadRom(new byte[] { 0x12, 0x34, 0x56 });
+        Assert.Equal(0x12, machine.memory[0x200]);
+        Assert.Equal(0x34, machine.memory[0x201]);
+        Assert.Equal(0x56, machine.memory[0x202]);
+    }
+
+    [Fact]
+    public void loadRomRejectsOversizedImage()
+    {
+        var machine = new Machine(Quirks.modern(), 1);
+        Assert.Throws<ArgumentException>(() => machine.loadRom(new byte[Machine.memorySize]));
+    }
+
+    [Fact]
+    public void delayAndSoundTimersCountDownAndGateBeep()
+    {
+        var machine = TestHarness.withOpcode(0xF018);
+        machine.v[0] = 3;
+        machine.step();
+        Assert.Equal(3, machine.soundTimer);
+        Assert.True(machine.soundActive);
+
+        machine.tickTimers();
+        machine.tickTimers();
+        machine.tickTimers();
+        Assert.Equal(0, machine.soundTimer);
+        Assert.False(machine.soundActive);
+
+        machine.tickTimers();
+        Assert.Equal(0, machine.soundTimer);
+    }
+
+    [Fact]
+    public void readDelayTimerIntoRegister()
+    {
+        var machine = TestHarness.withOpcode(0xF007);
+        machine.delayTimer = 0x2A;
+        machine.step();
+        Assert.Equal(0x2A, machine.v[0]);
+    }
+
+    [Fact]
+    public void addToIndex()
+    {
+        var machine = TestHarness.withOpcode(0xF01E);
+        machine.i = 0x200; machine.v[0] = 0x05;
+        machine.step();
+        Assert.Equal(0x205, machine.i);
+    }
+
+    [Fact]
+    public void fontCharacterAddress()
+    {
+        var machine = TestHarness.withOpcode(0xF029);
+        machine.v[0] = 0xB;
+        machine.step();
+        Assert.Equal(0x50 + 0xB * 5, machine.i);
+        Assert.Equal(0xE0, machine.memory[machine.i]);
+    }
+
+    [Fact]
+    public void binaryCodedDecimal()
+    {
+        var machine = TestHarness.withOpcode(0xF033);
+        machine.i = 0x300; machine.v[0] = 234;
+        machine.step();
+        Assert.Equal(2, machine.memory[0x300]);
+        Assert.Equal(3, machine.memory[0x301]);
+        Assert.Equal(4, machine.memory[0x302]);
+    }
+
+    [Fact]
+    public void storeAndLoadRegistersHonourIncrementQuirk()
+    {
+        var modern = TestHarness.withOpcode(0xF255, Quirks.modern());
+        modern.i = 0x300;
+        modern.v[0] = 0xAA; modern.v[1] = 0xBB; modern.v[2] = 0xCC;
+        modern.step();
+        Assert.Equal(0xAA, modern.memory[0x300]);
+        Assert.Equal(0xBB, modern.memory[0x301]);
+        Assert.Equal(0xCC, modern.memory[0x302]);
+        Assert.Equal(0x300, modern.i);
+
+        var cosmac = TestHarness.withOpcode(0xF265, Quirks.cosmacVip());
+        cosmac.i = 0x300;
+        cosmac.memory[0x300] = 0x11; cosmac.memory[0x301] = 0x22;
+        cosmac.step();
+        Assert.Equal(0x11, cosmac.v[0]);
+        Assert.Equal(0x22, cosmac.v[1]);
+        Assert.Equal(0x303, cosmac.i);
+    }
+
+    [Fact]
+    public void systemAddressOpcodeIsInert()
+    {
+        var machine = TestHarness.withOpcode(0x0123);
+        machine.step();
+        Assert.Equal(0x202, machine.pc);
+    }
+}
diff --git a/tests/Chip8.Tests/RomTests.cs b/tests/Chip8.Tests/RomTests.cs
new file mode 100644
index 0000000..5bd1703
--- /dev/null
+++ b/tests/Chip8.Tests/RomTests.cs
@@ -0,0 +1,36 @@
+using Chip8.Core;
+using Xunit;
+
+namespace Chip8.Tests;
+
+public class RomTests
+{
+    [Theory]
+    [InlineData("2-ibm-logo.ch8", 40, "ibm.txt", 230)]
+    [InlineData("3-corax+.ch8", 500, "corax.txt", 503)]
+    [InlineData("4-flags.ch8", 1000, "flags.txt", 495)]
+    [InlineData("test_opcode.ch8", 3000, "opcode.txt", 626)]
+    [InlineData("BC_test.ch8", 4000, "bctest.txt", 172)]
+    public void romRendersExpectedFramebuffer(string rom, int cycles, string golden, int litPixels)
+    {
+        var machine = TestHarness.runRom(rom, cycles);
+        string rendered = AsciiScreen.render(machine.display);
+
+        Assert.Equal(litPixels, AsciiScreen.litPixelCount(machine.display));
+        Assert.Equal(TestHarness.goldenText(golden), rendered);
+    }
+
+    [Fact]
+    public void corax89PassesUnderCosmacQuirksToo()
+    {
+        var machine = TestHarness.runRom("test_opcode.ch8", 3000, Quirks.cosmacVip());
+        Assert.Equal(TestHarness.goldenText("opcode.txt"), AsciiScreen.render(machine.display));
+    }
+
+    [Fact]
+    public void beepRomActivatesSoundTimer()
+    {
+        var machine = TestHarness.runRom("7-beep.ch8", 40);
+        Assert.True(machine.soundActive);
+    }
+}