test(core): add quirks and save-state tests

tests/Chip8.Tests/QuirksTests.cs

@@ -0,0 +1,104 @@
+using Chip8.Core;
+using Xunit;
+
+namespace Chip8.Tests;
+
+public class QuirksTests
+{
+    static Machine drawRowAt(int originX, Quirks quirks)
+    {
+        var machine = new Machine(quirks, 1);
+        machine.memory[0x200] = 0xD0;
+        machine.memory[0x201] = 0x11;
+        machine.i = 0x300;
+        machine.memory[0x300] = 0xFF;
+        machine.v[0] = (byte)originX;
+        machine.v[1] = 0;
+        machine.step();
+        return machine;
+    }
+
+    [Fact]
+    public void clipQuirkTruncatesSpriteAtRightEdge()
+    {
+        var clipping = new Quirks { clipSprites = true };
+        var machine = drawRowAt(62, clipping);
+        Assert.Equal(2, AsciiScreen.litPixelCount(machine.display));
+        Assert.True(machine.display[62]);
+        Assert.True(machine.display[63]);
+        Assert.False(machine.display[0]);
+    }
+
+    [Fact]
+    public void wrapQuirkWrapsSpriteAroundRightEdge()
+    {
+        var wrapping = new Quirks { clipSprites = false };
+        var machine = drawRowAt(62, wrapping);
+        Assert.Equal(8, AsciiScreen.litPixelCount(machine.display));
+        Assert.True(machine.display[62]);
+        Assert.True(machine.display[63]);
+        Assert.True(machine.display[0]);
+        Assert.True(machine.display[5]);
+        Assert.False(machine.display[6]);
+    }
+
+    [Fact]
+    public void shiftQuirkSelectsSourceRegister()
+    {
+        var usesVx = TestHarness.withOpcode(0x8016, new Quirks { shiftUsesVy = false });
+        usesVx.v[0] = 0b0000_0100;
+        usesVx.v[1] = 0xFF;
+        usesVx.step();
+        Assert.Equal(0b0000_0010, usesVx.v[0]);
+
+        var usesVy = TestHarness.withOpcode(0x8016, new Quirks { shiftUsesVy = true });
+        usesVy.v[0] = 0x00;
+        usesVy.v[1] = 0b0000_0100;
+        usesVy.step();
+        Assert.Equal(0b0000_0010, usesVy.v[0]);
+    }
+
+    [Fact]
+    public void loadStoreIncrementQuirkAdvancesIndex()
+    {
+        var noIncrement = TestHarness.withOpcode(0xF255, new Quirks { loadStoreIncrementsI = false });
+        noIncrement.i = 0x300;
+        noIncrement.step();
+        Assert.Equal(0x300, noIncrement.i);
+
+        var increment = TestHarness.withOpcode(0xF255, new Quirks { loadStoreIncrementsI = true });
+        increment.i = 0x300;
+        increment.step();
+        Assert.Equal(0x303, increment.i);
+    }
+
+    [Fact]
+    public void jumpQuirkSelectsOffsetRegister()
+    {
+        var withV0 = TestHarness.withOpcode(0xB300, new Quirks { jumpWithVx = false });
+        withV0.v[0] = 0x10;
+        withV0.v[3] = 0x20;
+        withV0.step();
+        Assert.Equal(0x310, withV0.pc);
+
+        var withVx = TestHarness.withOpcode(0xB300, new Quirks { jumpWithVx = true });
+        withVx.v[0] = 0x10;
+        withVx.v[3] = 0x20;
+        withVx.step();
+        Assert.Equal(0x320, withVx.pc);
+    }
+
+    [Fact]
+    public void vfResetQuirkClearsFlagOnLogic()
+    {
+        var noReset = TestHarness.withOpcode(0x8011, new Quirks { resetVfOnLogic = false });
+        noReset.v[0xF] = 0x5;
+        noReset.step();
+        Assert.Equal(0x5, noReset.v[0xF]);
+
+        var reset = TestHarness.withOpcode(0x8011, new Quirks { resetVfOnLogic = true });
+        reset.v[0xF] = 0x5;
+        reset.step();
+        Assert.Equal(0, reset.v[0xF]);
+    }
+}