test(core): add machine state and ROM loading tests

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);
+    }
+}